diff --git a/TCL/polarDensity_for_DTA.tcl b/TCL/polarDensity_for_DTA.tcl
index 29b9f66..9018a52 100644
--- a/TCL/polarDensity_for_DTA.tcl
+++ b/TCL/polarDensity_for_DTA.tcl
@@ -287,7 +287,7 @@ proc leaflet_sorter_3 {atsel_in frame_i} {
     set lipid_y [lindex $lipid_com 1]
     set lipid_z [lindex $lipid_com 2]
     
-    set local_surfaces [atomselect top "name PO4 GL1 GL2 AM1 AM2 and (x-$lipid_x)*(x-$lipid_x)+(y-$lipid_y)*(y-$lipid_y)<200" frame $frame_i]
+    set local_surfaces [atomselect top "name PO4 GL1 GL2 AM1 AM2 and pbwithin 200 of $atsel_in" frame $frame_i]
     set local_midplane [lindex [measure center $local_surfaces weight mass] 2]
     $local_surfaces delete