They way you're describing fore-aft is the way modern bike fitters do it. KOPS and plumb bobs are and always have been BS. There isn't even one particular optimal position for a given person. So any "formula" that claims to have the answer is wrong, right off the bat.
I see fore-aft as a tradeoff. More rearward is better for cruising, like on beach cruisers. Forward is better for hammering like on track bikes or TT bikes.