I meant you should look into a more efficient way of providing good cover for aliens and their structures than crates especially if you're just going to put 1 layer on the ground. 1 crate doesn't block much sight but can block alien movements terribly.
There is a very wide choice of what you can use, pillars, pipes, hanging lights, ceiling supports, ...
The most important is to player clip (or caulk, which has sensibly the same function aside from blocking bullets, but isn't rendered) everything properly if you have more complex shapes.
Try to make building require a bit more creativity, I don't know, make it funnier to build than just putting eggs in slots in the walls, trappers on the wall next to door, make people use their imaginations.