I was thinking of maybe putting more wall my side and / or having some bastions on my side. So might be best to map the top of the wall right up to the line (and a smidge over the line) in this case and not attempt to draw the front face of the wall at all. Then I can match up with that and do the front face in my area. Would be much easier than having detail right on the border which might get lost as part of the sector clipping. The wall needs to be about 20' thick anyway so we can have 10' each side of the sector boundary.