Wow...that's completely impractical. For the effort all that would take I'm not sure there's much benefit. You'd literally have to measure every board you were interested in. I have a hard enough time determining what I want already. Think about how limiting this would be. Imagine your favorite board with a reported waist width didn't match the your foot length. Then you couldn't get the board. Ok, so you might argue 1 or 2 millimeters doesn't make that much of a difference, just determine your range. So then what's the point of this at all? If you're looking to get into a millimeter range, just use waist width as a guide and know there will be a standard variation based on differences in geometry. You're essentially wasting your time even thinking about this.
PS - And where is the common sense in all of this?
Anyone who rides boilerplate regularly knows ideally you want as narrow a board as possible for quickest edge to edge transfer. But that same board is going to leave you hanging up at every turn in powder. Riding conditions aren't figured into this equation which are more practically significant than the predetermined geometrical theory you've proposed. Just sayin.
I think that's the whole point of the exercise, isn't it? To find a board that is both narrow enough to provide great leverage, while not being too narrow to create drag. That's the common sense in all of this.
I wear 7.5 boots and that fucks me out of a lot of the wider boards. Hell I hopped on a Coda 153 and you could BARELY see my boots from underneath the board. But I never noticed any sluggishness on hardpack/ice.
It's a guideline but unless you're in a perfectly narrow range, it isn't going to be black and white.