I've found some worked examples (from 2012):
https://www.aircraftinteriorsinterna...art-three.html
I've only skimmed it (not *that* interested) but the take-home is that on a short-haul flight a very *heavy* passenger will add about six dollars to the fuel cost compared to the average passenger, and the very *light* passenger will cost about five dollars less. This is neither here nor there when compared to the variations in ticket price due to time of purchase.
Arguably - as height and weight and size correlate - the light, short, passenger is amply compensated for their five dollars by having a seat that is relatively large and comfortable. And the tall, heavy, passenger pays for their six dollar "discount" by having a seat that is too small for them.
Those of us who are both lighter than average and taller than average get the worst deal.
Aside - I have a friend who is *so* tall that he'd get upgraded at check-in to First Class, because it's simply impossible to fold him into an economy seat.