Grinding my gears for years now. I've complained in the Beta, but to no avail. Still no ETA for a fix in sight.
The zone only cares for the reference lines of the walls as a bounding. So the trick is to have those still join up, even if you "patch" over it with the column. This will look fine in 2D and 3D. Luckily the zone will then still find the outline of the column (as long its settings are correct) and thus everything will be fine, even with protruding columns. No need for 2D lines.
Lucas Becker | Mostly AC 26 on Mac | Author of SelfGDL | Developer of the GDL plugin for Sublime Text | «Furthermore, I consider that Carth... yearly releases must be destroyed»