It may be getting "too technical", but chamber diameter and depth mean little when the bowl has a sharp TAPER (bulldogs, Kirstens, etc.).
Also, a tall, narrow "stack" will smoke/taste differently than a squatty pot, even tho' they have the same tobacco volume.
Add these variables to the variations in tobaccos and in packing and you are trying to solve a formula that would confound Einstein. :D