I, too, place all of my mixers on the bottom row. However, after thinking about it, I think the top row would be best and the Behr may be on to something! With the jacks on the bottom and the modules in the top row, all cables would be completely out of the way. When the mixers are on bottom row, we still have to deal with all the sagging cables that sort of pool at the bottom from all the action in the rest of the case.
Something to think about....

over:under