The pedals/crank go round in a circle, that's pretty much a 'gimmie', Other than that I don't think there is a "one-size-fits-perfectly" formula or definition for everyone. But if you ride with the balls of your feet on the pedals, and you trace out your ankle's path as it goes around, then it probably has a slight elliptical pattern. I couldn't tell you about shorter crank arms and their relation to saddle adjustments, but I did put shorter cranks (170 from 175) on my bicycles and it relieved a lot of joint 'aches' (not pain) in my knees, and it reduced the amount of saddle adjustments I was always making in search of the 'holy grail' spot for comfort. I still adjust my saddle occasionally, but not near as much as before. It really is dependent on the individual person's bio-geometry and bio-mechanics, you just have to fiddle with it to find a comfortable zone of crank arm length and saddle height/position. .