diff --git a/GeometryService/src/MECOStyleProtonAbsorberMaker.cc b/GeometryService/src/MECOStyleProtonAbsorberMaker.cc
index 9bf595e5bc..a39221223a 100644
--- a/GeometryService/src/MECOStyleProtonAbsorberMaker.cc
+++ b/GeometryService/src/MECOStyleProtonAbsorberMaker.cc
@@ -125,6 +125,14 @@ namespace mu2e {
     // we add space for the virtual detector here
     double targetEnd = _target->centerInMu2e().z() + 0.5*_target->cylinderLength() + 2.*vdHL;;
 
+    // Optional absolute pinning: when protonabsorber.zStartInMu2e is set,
+    // the IPA's upstream end sits at that absolute z regardless of the
+    // stopping target; distFromTargetEnd then only anchors the cone-radius
+    // interpolation. Unset (default): stock target-relative behavior.
+    if ( _config.hasName("protonabsorber.zStartInMu2e") ) {
+      targetEnd = _config.getDouble("protonabsorber.zStartInMu2e") - distFromTargetEnd;
+    }
+
     // distance from target end to ds2-ds3 boundary
     double targetEndToDS2End = _ds->vac_zLocDs23Split() - targetEnd;
 
diff --git a/Mu2eG4/geom/protonAbsorber_cylindrical_v04.txt b/Mu2eG4/geom/protonAbsorber_cylindrical_v04.txt
index 673904b182..4cedf0fa6e 100644
--- a/Mu2eG4/geom/protonAbsorber_cylindrical_v04.txt
+++ b/Mu2eG4/geom/protonAbsorber_cylindrical_v04.txt
@@ -29,6 +29,9 @@ bool   protonabsorber.solid        = false;
 // To make inner part shorter than MECO design
 bool   protonabsorber.isShorterCone = true;
 double protonabsorber.distFromTargetEnd = 625.; //mu2e z positions are 6901-7901 mm
+// Optional: pin the IPA at an absolute z, independent of the stopping
+// target (see MECOStyleProtonAbsorberMaker):
+// double protonabsorber.zStartInMu2e = 6901.;
 double protonabsorber.halfLength   = 500.0;
 
 bool   protonabsorber.ipa.buildSupports = true;