I'm willing to bet that the highest earning Captain of a family makes more money than the Underboss. An Underboss has it easy since he always gets a cut from below and maybe a profitable racket or two, but a Captain with a large crew for earners under him and some union control will make a shitload with only a percentage being kicked up.

And 50% seems WAY too high for a associate/soldier to kick up to a captain or for a captain to kick up to the administration.