I think it all depends upon what time of the year you want to use your cribs. How deep is the deepest water? Are there drop offs near the 20 foot range? If your going to be fishing them in the spring and fall why not move them shallower. You'll get the fish twice each year. Once on the way into spawn and when they are leaving the spawning areas. Then again in the fall when they go on there feeding spree just before winter. If you place them real shallow they may only be good in the spring, and too deep they may work in summer, if there is enough oxygen at 20 feet and again in winter. All the brush I sink I try to place it in the mid depth range, my lake is only 30 feet deep and has alot of drop offs at the 12-15 foot depth. That's where I put mine.