diff --git a/inc/TRestAxionTrueWolterOptics.h b/inc/TRestAxionTrueWolterOptics.h
index b8ba4ba0..1677f348 100644
--- a/inc/TRestAxionTrueWolterOptics.h
+++ b/inc/TRestAxionTrueWolterOptics.h
@@ -47,6 +47,9 @@ class TRestAxionTrueWolterOptics : public TRestAxionOptics {
     /// Mirror thickness in mm. See schematic figure.
     std::vector<Double_t> fThickness;  //!
 
+    /// Distance between mirror stacks in mm. See schematic figure.
+    std::vector<Double_t> fXSep;  //!
+
     /// The spider structure to be used as an optical opaque mask (common to all planes)
     TRestSpiderMask* fSpiderMask = nullptr;  //<
 
@@ -110,13 +113,13 @@ class TRestAxionTrueWolterOptics : public TRestAxionOptics {
 
     /// It returns the entrance Z-position defined by the optical axis.
     Double_t GetEntrancePositionZ() override {
-        if (fCosAlpha.size() > 0) return -fMirrorLength * fCosAlpha[0];
+        if (fCosAlpha.size() > 0) return -fMirrorLength * fCosAlpha[0] - 0.5 * fXSep[0];
         return 0;
     }
 
     /// It returns the exit Z-position defined by the optical axis
     Double_t GetExitPositionZ() override {
-        if (fCosAlpha_3.size() > 0) return fMirrorLength * fCosAlpha_3[0];
+        if (fCosAlpha_3.size() > 0) return fMirrorLength * fCosAlpha_3[0] + 0.5 * fXSep[0];
         return 0;
     }
 
diff --git a/inc/TRestAxionWolterOptics.h b/inc/TRestAxionWolterOptics.h
index eb1e837a..eaf00243 100644
--- a/inc/TRestAxionWolterOptics.h
+++ b/inc/TRestAxionWolterOptics.h
@@ -47,6 +47,9 @@ class TRestAxionWolterOptics : public TRestAxionOptics {
     /// Mirror thickness in mm. See schematic figure.
     std::vector<Double_t> fThickness;  //!
 
+    /// Distance between mirror stacks in mm. See schematic figure.
+    std::vector<Double_t> fXSep;  //!
+
     /// The spider structure to be used as an optical opaque mask (common to all planes)
     TRestSpiderMask* fSpiderMask = nullptr;  //<
 
@@ -110,13 +113,13 @@ class TRestAxionWolterOptics : public TRestAxionOptics {
 
     /// It returns the entrance Z-position defined by the optical axis.
     Double_t GetEntrancePositionZ() override {
-        if (fCosAlpha.size() > 0) return -fMirrorLength * fCosAlpha[0];
+        if (fCosAlpha.size() > 0) return -fMirrorLength * fCosAlpha[0] - 0.5 * fXSep[0];
         return 0;
     }
 
     /// It returns the exit Z-position defined by the optical axis
     Double_t GetExitPositionZ() override {
-        if (fCosAlpha_3.size() > 0) return fMirrorLength * fCosAlpha_3[0];
+        if (fCosAlpha_3.size() > 0) return fMirrorLength * fCosAlpha_3[0] + 0.5 * fXSep[0];
         return 0;
     }
 
diff --git a/src/TRestAxionTrueWolterOptics.cxx b/src/TRestAxionTrueWolterOptics.cxx
index 592c5ba0..c4e23898 100644
--- a/src/TRestAxionTrueWolterOptics.cxx
+++ b/src/TRestAxionTrueWolterOptics.cxx
@@ -174,6 +174,11 @@ void TRestAxionTrueWolterOptics::Initialize() {
     fAlpha = GetAlpha();
     fThickness = GetThickness();
 
+    fXSep.clear();
+    for (unsigned int n = 0; n < fAlpha.size(); n++)
+        fXSep.push_back(2 * (fR1[n] - fR3[n] - fMirrorLength * TMath::Sin(fAlpha[n])) /
+                        TMath::Tan(fAlpha[n]));
+
     if (fAlpha.size() == 0) return;
 
     fCosAlpha.clear();
@@ -276,9 +281,10 @@ Int_t TRestAxionTrueWolterOptics::FirstMirrorReflection(const TVector3& pos, con
 
     //// Reflection on first mirror
     fFirstInteractionPosition = REST_Physics::GetParabolicVectorIntersection(
-        pos, dir, fAlpha[mirror], fR3[mirror], fMirrorLength);  // should add this: TVector3(0, 0, -1), vertex
+        pos, dir, fAlpha[mirror], fR3[mirror]);  // should add this: TVector3(0, 0, -1), vertex
 
-    if (fFirstInteractionPosition.Z() < GetEntrancePositionZ() || fFirstInteractionPosition.Z() > 0) {
+    if (fFirstInteractionPosition.Z() < GetEntrancePositionZ() ||
+        fFirstInteractionPosition.Z() > -(0.5 * fXSep[mirror])) {
         RESTDebug << "TRestAxionTrueWolterOptics::FirstMirrorReflection. No interaction!" << RESTendl;
         fFirstInteractionPosition = REST_Physics::MoveByDistance(pos, dir, fMirrorLength / 2.);
         fMiddleDirection = fEntranceDirection;
@@ -321,12 +327,12 @@ Int_t TRestAxionTrueWolterOptics::SecondMirrorReflection(const TVector3& pos, co
     TVector3 vertex(0, 0, fBackVertex[mirror]);
     Double_t focal = fR3[mirror] / TMath::Tan(4 * fAlpha[mirror]);
 
-    //// Reflection on first mirror
-    fSecondInteractionPosition =
-        REST_Physics::GetHyperbolicVectorIntersection(pos, dir, fAlpha[mirror], fR3[mirror], fMirrorLength,
-                                                      focal);  // should add this: TVector3(0, 0, -1), vertex,
+    //// Reflection on second mirror
+    fSecondInteractionPosition = REST_Physics::GetHyperbolicVectorIntersection(
+        pos, dir, fAlpha[mirror], fR3[mirror], focal);  // should add this: TVector3(0, 0, -1), vertex,
 
-    if (fSecondInteractionPosition.Z() > GetExitPositionZ() || fSecondInteractionPosition.Z() < 0) {
+    if (fSecondInteractionPosition.Z() > GetExitPositionZ() ||
+        fSecondInteractionPosition.Z() < (0.5 * fXSep[mirror])) {
         RESTDebug << "TRestAxionTrueWolterOptics::SecondMirrorReflection. No interaction!" << RESTendl;
         fSecondInteractionPosition = REST_Physics::MoveByDistance(pos, dir, fMirrorLength / 2.);
         fExitDirection = fMiddleDirection;
diff --git a/src/TRestAxionWolterOptics.cxx b/src/TRestAxionWolterOptics.cxx
index faac2445..14ce777b 100644
--- a/src/TRestAxionWolterOptics.cxx
+++ b/src/TRestAxionWolterOptics.cxx
@@ -174,6 +174,11 @@ void TRestAxionWolterOptics::Initialize() {
     fAlpha = GetAlpha();
     fThickness = GetThickness();
 
+    fXSep.clear();
+    for (unsigned int n = 0; n < fAlpha.size(); n++)
+        fXSep.push_back(2 * (fR1[n] - fR3[n] - fMirrorLength * TMath::Sin(fAlpha[n])) /
+                        TMath::Tan(fAlpha[n]));
+
     if (fAlpha.size() == 0) return;
 
     fCosAlpha.clear();
@@ -278,7 +283,8 @@ Int_t TRestAxionWolterOptics::FirstMirrorReflection(const TVector3& pos, const T
     fFirstInteractionPosition =
         pos + dir * REST_Physics::GetConeVectorIntersection(pos, dir, TVector3(0, 0, -1), vertex, cosA);
 
-    if (fFirstInteractionPosition.Z() < GetEntrancePositionZ() || fFirstInteractionPosition.Z() > 0) {
+    if (fFirstInteractionPosition.Z() < GetEntrancePositionZ() ||
+        fFirstInteractionPosition.Z() > -(0.5 * fXSep[mirror])) {
         RESTDebug << "TRestAxionWolterOptics::FirstMirrorReflection. No interaction!" << RESTendl;
         fFirstInteractionPosition = REST_Physics::MoveByDistance(pos, dir, fMirrorLength / 2.);
         fMiddleDirection = fEntranceDirection;
@@ -323,7 +329,8 @@ Int_t TRestAxionWolterOptics::SecondMirrorReflection(const TVector3& pos, const
     fSecondInteractionPosition =
         pos + dir * REST_Physics::GetConeVectorIntersection(pos, dir, TVector3(0, 0, -1), vertex, cosA);
 
-    if (fSecondInteractionPosition.Z() > GetExitPositionZ() || fSecondInteractionPosition.Z() < 0) {
+    if (fSecondInteractionPosition.Z() > GetExitPositionZ() ||
+        fSecondInteractionPosition.Z() < (0.5 * fXSep[mirror])) {
         RESTDebug << "TRestAxionWolterOptics::SecondMirrorReflection. No interaction!" << RESTendl;
         fSecondInteractionPosition = REST_Physics::MoveByDistance(pos, dir, fMirrorLength / 2.);
         fExitDirection = fMiddleDirection;