Wooden seats or wooden supports can be flipped into the air with Shift-right-click. I have a few problems with that: Firstly, this mechanic doesn't exist in vanilla Minecraft and secondly, Every Combat also has problems with it (item model is not reversed, but block is).
My suggestion would therefore be:

Wooden supports have the same placement as normal stairs. On the lower side of a block (wall) the support lies on the ground, on the upper half it hangs; place it on the top of a block and it lies, place it on the bottom and it hangs.

Wooden seats, on the other hand, can be raised to the top by shift-right-clicking (that you don't sit down).

These changes don't have to be accepted, I just think it would be nicer this way.