I just bought some used jumpers (70" Kidders) and I want to make sure I get the bindings in the right spot. These skis have only had one set of bindings on them since new, and they're about 1" forward compared to a friend's 70" Kidder skis. Is there a rule of thumb for binding mounting? For reference, I measured the total ski length at 69.5" and the back side of the Wiley binding plate to the back of the ski is 27.5". Does that sound reasonable? While skiing, the waterline is basically at/under my feet.