I saw on Skis.com that they classify instep height of ski boots according to the following scale:
Low: circumference of instep <1/3 the length of your foot
Medium: circumference of instep 1/3 to 1/2 the length of your foot
High: circumference of instep >1/2 the length of your foot
However, they do not describe how to measure “circumference of instep”. I tried several different measurements, and the only one that seems to make sense with these definitions is straight up from the floor, over the highest part of the instep, and back down to the floor.
(Other possible interpretations are tape wrapped fully around foot at instep, or from heel over instep and back to heel, both of which are approximately equal to the foot length and don't make sense with those definitions).
Am I doing this measurement correctly? It puts me at (instep circumference)/(foot length) = 0.7, so well into the “high” instep category. If true, this is kind of a revelation for me as I always thought I had normal to low instep height.
I know somebody will say "go see a bootfitter", which is of course the right answer, but I want to do my own research first.