Spawning Procedural Foliage on Static Meshes

Hello, I’m creating a map WITHOUT a generated terrain, and instead I’m using my own static mesh tiles. On top of the tiles I am attempting to use a Procedural Foliage volume to generate the plants, but it refuses to spawn on some tiles, while working fine on others. Each tile comes from the same parent blueprint, so there are no major differences.

Also, interestingly, the foliage will spawn on tile pieces ROTATED specific angles and not others.

These 3 tiles are the EXACT SAME piece, but the foliage only spawns if they’re rotated that way.

Other things I’ve noticed: foliage may still spawn, but only on edges and slopes. Not flat surfaces. So when I rotate my whole map 1 degrees on the x or y axis, the foliage will spawn everywhere. I think this is a clue. Somewhere, there must be a setting to allow foliage to spawn on these flat surfaces.
I have no idea why it’s behaving like this and I would appreciate any help.

Thanks in advance.