Nicanor said:
"I would think that the puck on top of the weight block would increase the dif more. Make it more of a flip ball. the weight block might add dif, but whats the difference between a puck on the bottom of a weight block as compared to a puck on top of the weight block, of course using the same weight block and ball."

Typically a weight block on the top causes more of a flip reaction where as putting the weight block on the bottom creates more of a roller reaction. A secondary issue would be weight blocks on top, depending on shape, could get drilled into for the holes, so it is a less reliable location since the holes will change its weight.