Well so far I've got around it by putting floor decals on a different layer with a Z elevation 0.01 higher than the map layer and used line of sight to cast a ray for wall decals on creation to stick them to the coordinates they hit but 0.1 away from the wall that they're Z elevation is going to match.
I feel like this is one of the worst solutions for this and I don't like it, but it seems to work. If anyone has any better ideas, please let me know.
I'm basically using the 3D first person platformer example but I've expanded it far beyond its original scope where multiple actors can be handled instead of only the player, slopes(wedges), ability to aim attacks up and down, etc.