Generally speaking, and I hope this doesn't sound cynical, but if you are a new and unknown quantity to a prop firm and you decide to put up say $25-50K so as to get a bigger split of the profits (90-100%), wouldn't the firm likely cut you loose if you lost your stake, before the firm was in too much of a position of losing their own capital? So effectively, their "backing you" for leverage purposes only (and of course to make commissions)