Please help with mounting a bathroom mirror
This is how you handle French Cleats so they don't stand the piece off the wall. They are inset into the back by extending all the edges rearward by exactly the thickness of the cleat material.
Yes, you can use cleats top and bottom, but you need to be ever so precise in your placement of them. Get off even a tiny bit, and things get sloppy in the fit department.
"True eloquence consists in saying all that is necessary, and only that which is."
François Duc de La Rochefoucauld