Collision Detection in FF6LE

When I make map edits in FF6LE (or Zone Doctor, prior), I'm having problems getting collision to work correctly when rearranging objects. The objects I'm having trouble with are the ones where you can walk on the tile from the top, but not the bottom. Examples include chairs, pots, etc. When I place these objects, my character sprite briefly clips behind the objects, then pops up on top. I've tried everything I can think of, but have had to resort to creating an invisible wall 1 tile below the objects when possible so that nobody can notice this graphical error. Has anyone encountered this issue? What did you do to work around it?