The wall has GG potential at the GG level. It is grounded on the side facing iTPC and biased with -690 V on the side facing oTPC.
It is 2.5 mm away from the last GG wire.
In addition here I shifter the polarity of GG by one wire, meaning the wire next to the wall now has 140 v difference from one in V31 version which is also below for comparison.
You can see how wires on which leak is focused shifts one wire, in both inner and outer side. It looks like outer leak is greatly affected by this. So one way to reduce the outer leak would be to make sure outer part last wire potential is less then one next to it.