Nice blog wiredsport, a gift to us all!
You guys left out board taper too, as a factor of measurement.
I will only add the reason no measurements are taken at the inserts is people adjust stances, so you would need an entire separate graph of all combinations, not practical. Also, stance angles completely change the measurements and overhang.
That is buried in there around the middle
. Stance angle is really easy to factor in:
"how do you interpret this info to get the correct width? Well that depends a little on stance angle. If you ride a 0 degree stance, you will want your foot size to be the same as the width of the board at the inserts or up to 1 cm greater. If you ride at an angled stance, you will want to measure the board across at the angles that you will be riding. Again, you will want your foot to at least match this measurement or exceed it by up to 1 cm."