Thanks for your help! I never quite understood those priority settings before, but now I get it! Same thing will work if there's plaster or insulation, etc. Highest priority overrides lower ones. Thanks.
As for the wall end tool, that helps, but doesn't work around openings.. I managed to solve the problem though by doing a little more fiddling and searching and there's actually a setting in the door or window itself not the wall which fixes it.
Image attached for future reference.
Cape Town, South Africa
AC 24
Windows 10
Intel Core i3-4160 3.6GHz
NVidia GeForce GTX 1660 SUPER