diff --git a/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/MuonReadoutGeometry/RpcReadoutElement.h b/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/MuonReadoutGeometry/RpcReadoutElement.h
index df9d7988f5f7f732f7a385959179b81be610b45e..dfdeac284e754698fb08d8f0cc3885032a879de7 100644
--- a/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/MuonReadoutGeometry/RpcReadoutElement.h
+++ b/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/MuonReadoutGeometry/RpcReadoutElement.h
@@ -248,7 +248,7 @@ namespace MuonGM {
 
     int m_dbR, m_dbZ, m_dbPhi;
     bool m_hasDEDontop;
-    int m_nlayers;  // default=2, all BIS RPCs always have 3 gas gaps
+    int m_nlayers;  // default=2, all BI RPCs always have 3 gas gaps, need this flag since amdb only supports a maximum of 2 gas gaps, so this is steering the hardcoded third gas gap for Run3/4 layouts based on amdb primary numbers
 
     int m_nphigasgaps;
     int m_netagasgaps;
diff --git a/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/src/RpcReadoutElement.cxx b/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/src/RpcReadoutElement.cxx
index c9c6da5e5e5e80173ca8b168a4270707b3e6abc3..aff1cc3bf4392657fb588d4705ac937ba7b52f22 100644
--- a/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/src/RpcReadoutElement.cxx
+++ b/MuonSpectrometer/MuonDetDescr/MuonReadoutGeometry/src/RpcReadoutElement.cxx
@@ -307,8 +307,8 @@ namespace MuonGM {
   {
     const GenericRPCCache* r = manager()->getGenericRpcDescriptor();
     double xgg=0;
-    if (m_nlayers==3) { // the BIS RPCs are the only ones with 3 gas gaps, they don't have an inner support structure
-      xgg = -rpc3GapLayerThickness + (gasGap-1)*rpc3GapLayerThickness - 0.74; // the values from MuonGeoModel have an offset of 0.74, TO BE INVESTIGATED
+    if (m_nlayers==3) { // the BI RPCs are the only ones with 3 gas gaps, they don't have an inner support structure
+      xgg = -rpc3GapLayerThickness + (gasGap-1)*rpc3GapLayerThickness - 0.74; // the values from MuonGeoModel have an offset of 0.74, TO BE INVESTIGATED, cf. ATLASSIM-5021
     } else {
       xgg = -m_Rsize/2. + m_exthonthick + r->stripPanelThickness + r->GasGapThickness/2.;
       if (gasGap == 1) return xgg;
diff --git a/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetectorCosmics_gtest.cxx b/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetectorCosmics_gtest.cxx
index f56e7ad2ae18a59af13949f5602736612ca5c545..2967a3839cadcaa95341363717e8619e73d6a61c 100644
--- a/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetectorCosmics_gtest.cxx
+++ b/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetectorCosmics_gtest.cxx
@@ -38,7 +38,7 @@ class RPCSensitiveDetectorCosmicstest : public ::testing::Test {
 TEST_F ( RPCSensitiveDetectorCosmicstest, Initialize )
 {
   G4HCofThisEvent hce;
-  RPCSensitiveDetectorCosmics sd1("name1", "name1", 2); // name, hitCollectionName, nGasGaps; all non-BIS RPCs (Run1+2) have 2 gas gaps, only BIS RPCs have 3 gas gaps
+  RPCSensitiveDetectorCosmics sd1("name1", "name1", 2); // name, hitCollectionName, nGasGaps; all non-BI RPCs (Run1+2) have 2 gas gaps, only BI RPCs have 3 gas gaps
   sd1.Initialize( &hce );
   ASSERT_TRUE(sd1.m_myRPCHitColl.isValid()); //check if initialization of m_myRPCHitColl is successful
 }
@@ -74,7 +74,7 @@ TEST_F ( RPCSensitiveDetectorCosmicstest, ProcessHits )
   G4String nop3 = "gamma";
   DerivedG4SensitiveDetectorTestSetting(sp, totalenergydeposit, physicalname, logicalname, copynos, preStepPos, postStepPos, globaltime0, kineticenergy0, velocity0, globaltime, kineticenergy, globaltime1, kineticenergy1, velocity1, steplength, charge, encoding, antiencoding, astring, atype, nop1, nop2, nop3);//invoking of this function aims to setting testing environment.
 
-  RPCSensitiveDetectorCosmics sd2("name2", "name2", 2); // name, hitCollectionName, nGasGaps; all non-BIS RPCs (Run1+2) have 2 gas gaps, only BIS RPCs have 3 gas gaps
+  RPCSensitiveDetectorCosmics sd2("name2", "name2", 2); // name, hitCollectionName, nGasGaps; all non-BI RPCs (Run1+2) have 2 gas gaps, only BI RPCs have 3 gas gaps
   sd2.Initialize( &hce );//initialize the hit collection m_myCSCHitColl
   sd2.ProcessHits(&sp, &th );//invoke the tested member function
 
diff --git a/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetector_gtest.cxx b/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetector_gtest.cxx
index d610d17e3634165b75100137dfca6f94ac9731e5..baed966739cc06906e6da62d632af67c88cc5366 100644
--- a/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetector_gtest.cxx
+++ b/MuonSpectrometer/MuonG4/MuonG4SD/test/RPCSensitiveDetector_gtest.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "src/RPCSensitiveDetector.h"
@@ -38,7 +38,7 @@ class RPCSensitiveDetectortest : public ::testing::Test {
 TEST_F ( RPCSensitiveDetectortest, Initialize )
 {
   G4HCofThisEvent hce;
-  RPCSensitiveDetector sd1("name1", "name1", 2); // name, hitCollectionName, nGasGaps; all non-BIS RPCs (Run1+2) have 2 gas gaps, only BIS RPCs have 3 gas gaps
+  RPCSensitiveDetector sd1("name1", "name1", 2); // name, hitCollectionName, nGasGaps; all non-BI RPCs (Run1+2) have 2 gas gaps, only BI RPCs have 3 gas gaps
   sd1.Initialize( &hce );
   ASSERT_TRUE(sd1.m_myRPCHitColl.isValid()); //check if initialization of m_myRPCHitColl is successful
 
@@ -75,7 +75,7 @@ TEST_F ( RPCSensitiveDetectortest, ProcessHits )
   G4String nop3 = "gamma";
   DerivedG4SensitiveDetectorTestSetting(sp, totalenergydeposit, physicalname, logicalname, copynos, preStepPos, postStepPos, globaltime0, kineticenergy0, velocity0, globaltime, kineticenergy, globaltime1, kineticenergy1, velocity1, steplength, charge, encoding, antiencoding, astring, atype, nop1, nop2, nop3);//invoking of this function aims to setting testing environment.
 
-  RPCSensitiveDetector sd2("name2", "name2", 2); // name, hitCollectionName, nGasGaps; all non-BIS RPCs (Run1+2) have 2 gas gaps, only BIS RPCs have 3 gas gaps
+  RPCSensitiveDetector sd2("name2", "name2", 2); // name, hitCollectionName, nGasGaps; all non-BI RPCs (Run1+2) have 2 gas gaps, only BI RPCs have 3 gas gaps
   sd2.Initialize( &hce );//initialize the hit collection m_myRPCHitColl
   sd2.ProcessHits(&sp, &th );//invoke the tested member function
 
diff --git a/MuonSpectrometer/MuonGeoModel/src/Rpc.cxx b/MuonSpectrometer/MuonGeoModel/src/Rpc.cxx
index c5ac1e35345bf4ca6c9540cb618c8dadc0eb0470..3e72f1eca58bac27ef8dd2b6ef8a702f152929ec 100644
--- a/MuonSpectrometer/MuonGeoModel/src/Rpc.cxx
+++ b/MuonSpectrometer/MuonGeoModel/src/Rpc.cxx
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "MuonGeoModel/Rpc.h"
@@ -79,7 +79,7 @@ namespace MuonGM {
         double centSupThick = r->centralSupPanelThickness;
         double centAlSupThick = r->centralAlSupPanelThickness;
 
-        // Geometrical information to be overwritten for BIS chambers (having 3 gas gaps)
+        // Geometrical information to be overwritten for BI chambers (having 3 gas gaps)
         if (m_nlayers == 3) {
             // width, longWidth, length are taken from geometry DB
             thickness = rpc3GapMaxThickness;
@@ -159,7 +159,7 @@ namespace MuonGM {
                 }
             }
 
-            if (m_nlayers == 2) { // only to be done for standard (non-BIS) RPCs
+            if (m_nlayers == 2) { // only to be done for standard (non-BI) RPCs
                 newpos += extSupThick / 2.;
                 GeoTransform *tlpan = new GeoTransform(GeoTrf::TranslateX3D(newpos));
                 if (RPCprint) {
@@ -170,7 +170,7 @@ namespace MuonGM {
                     prpc->add(pallpan);
                 }
 
-                // The first layer is support for RPCs with 2 gaps, is a layer for 3 gaps (BIS chambers, no supports)
+                // The first layer is support for RPCs with 2 gaps, is a layer for 3 gaps (BI chambers, no supports)
                 newpos += extSupThick / 2.;
             }
 
@@ -229,7 +229,7 @@ namespace MuonGM {
                 }
             }
 
-            if (m_nlayers == 2) { // only to be done for standard (non-BIS) RPCs
+            if (m_nlayers == 2) { // only to be done for standard (non-BI) RPCs
                 newpos += centSupThick / 2.;
                 GeoTransform *tcpan = new GeoTransform(GeoTrf::TranslateX3D(newpos));
                 if (RPCprint) {
@@ -307,11 +307,11 @@ namespace MuonGM {
                 prpc->add(new GeoIdentifierTag(2));
                 prpc->add(tugg);
                 if (m_nlayers == 2)
-                    prpc->add(rugg); // only to be done for standard (non-BIS) RPCs
+                    prpc->add(rugg); // only to be done for standard (non-BI) RPCs
                 prpc->add(puppergg);
             }
 
-            // additional RpcLayer for BIS (3 gaps)
+            // additional RpcLayer for BI (3 gaps)
             if (m_nlayers == 3) {
                 newpos += rpcLayerThickness / 2.;
                 RpcLayer *rthird = new RpcLayer(name, this);
diff --git a/MuonSpectrometer/MuonSimEvent/MuonSimEvent/RpcHitIdHelper.h b/MuonSpectrometer/MuonSimEvent/MuonSimEvent/RpcHitIdHelper.h
index 60ec487f6241f139297831e71729a9bd68820300..2d470d8744bbb5ac0ec2e0e5c27bd93f66a0c331 100644
--- a/MuonSpectrometer/MuonSimEvent/MuonSimEvent/RpcHitIdHelper.h
+++ b/MuonSpectrometer/MuonSimEvent/MuonSimEvent/RpcHitIdHelper.h
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef RpcHitIdHelper_H
@@ -31,7 +31,7 @@ public:
 private:
   RpcHitIdHelper();
   RpcHitIdHelper(unsigned int nGasGaps);
-  void Initialize(unsigned int nGasGaps=2); // all non-BIS RPCs (Run1+2) have 2 gas gaps, only BIS RPCs have 3 gas gaps
+  void Initialize(unsigned int nGasGaps=2); // all non-BI RPCs (Run1+2) have 2 gas gaps, only BI RPCs have 3 gas gaps
   void InitializeStationName();
   static RpcHitIdHelper* m_help;