I think that the standard split is as follows:
1)Associates kick up 50% of all profits to whichever soldier they are with.
2)Soldiers kick up 50% to whichever Capo they are under.
3)Capos kick up a weekly or monthly amount that is set by the Boss,and is whatever the Boss says it is.

Of course there are exceptions. Joe Pistone states that although the customary soldier/captain split is 50-50,captains,like anyone else are greedy and can set any rules they want for their crews.
Like much in the OC world,this is info that only true Made Guys can verify and I'm sure there are tons of exceptions.