I'm not sure if the equations are exact, but I'd definitely say weight loss makes a difference. I've lost a fair bit of weight in the last year, and things have definitely improved.
I can vouch for that. I have lost 92 pounds in a year, and my penis has grown quite a bit. Actually, it was always there, just surrounded by flab. I will never reach my navel though. (I actually was so fat that I had an "innie." It is nice to have an "outie" now.)