That would work well if the cards were unidirectional in their exhaust, like reference cards. Those cards pictured exhaust heat out of the front of them and the back. With the front less than 6" from the solid counter they're sitting on and some even more obscured by the PSU it is probably hindering their cooling ability. Try laying it horizontally, moving the PSU out of the way, and see if the temperature changes any. My guess is it makes a large difference.