How are they determined in relation to the map? I'm trying to have a multiple caves, and I'm having some trouble placing the Mats. Is it possible to just consolidate them into one huge Mat as large as the map itself is?

That sounds plausible. I believe bunkermodules have an offset at their center by default, either that or the upper left. Upper left sounds like it would be more likely.

It's centered. Thanks a bunch.