fix: increase backward_dz to fit ip6_extended

Author: wdconinc

compact/definitions.xml

@@ -12,7 +12,7 @@
     <constant name="backward_x0" value="0.5*m"/>
     <constant name="backward_dx" value="2*m"/>
     <constant name="backward_dy" value="1*m"/>
-    <constant name="backward_dz" value="35*m"/>
+    <constant name="backward_dz" value="40*m"/>
     <constant name="exp_hall_dx" value="3.5*m"/>
     <constant name="exp_hall_dy" value="3.5*m"/>
     <constant name="exp_hall_dz" value="5.5*m"/>