I was planning on a 1/2" or maybe a 3/4" cabinet back and attach the cabinet side of the cleat to the cabinet back. Leary of having the cleat supported by a 1/4" cabinet back and the cabinet top.
That's why I added a piece of 1x3 across the top of mines. I used 1/4" oak panels for my backs, and I knew that was to thin to support them. So I ran a 1x3 across the top, to screw my "modified French Cleats" to them. I didn't use the "French cleats" because of the two tapers. If I had to pull out a cabinet (because my walls weren't exactly straight/square) it also rase the cabinet. So I made cleats with loose rabbets. I hung all my cabinets, by myself, and no jacks or anything. Smooth sailing!!