Agreed. this might clarify or confuse more:
Your ankle is the constant, the difference of your bare foot and to where you measure at the "heel" of your binding is obviously how thick the binding is. So, if you find your ankle in your binding, mark it with a silver marker or whatever, find where you measure to on the binding, then just do the math. Bob's your uncle.
The big variable/unknown is who defines "stock" and how far their ankle is from their heel. If Joe Cash says, "29 5/8 is money", and I go to 29 5/8, my ankle is 1/2" too far forward (not money)