Purchased a pair of black leather hi tops (aka Mark Bell powerlifting shoe) when they first came out and liked them - especially for deadlifting.  I recently purchased the low tops as a replacement and noticed that I was losing my balance backwards.  I compared the new shoe to the old shoe and noticed a slight upward slant at the back of the heel.  I confirmed with Reebok that both the new hi tops and lo tops had the slight upward slant at the back of the heel in order to make them more usable for dynamic movements and not just powerlifting movements.  Since I had worn them, I could not return them so I will be using them for calf raises and dynamic movements while still using my old hi tops and looking for a replacement.