There's no reason behind it, and it has nothing to do with their humps. Dominate males will retain the largest hump - if you place two males in a small tank with a divider they will both attain large humps to compete with one another...that's how flowerhorns get such huge KOK's.
starve them 2 days a week so they dont get backed up from being fed soo much. other days feed them till they look like there gonna explode. is that what you were getting at cam?