[Siegmund]

I think it's a pretty raw deal for you, unless your partner is a spectacularly good player. In one sense you are "just doing 10% worse than he is", but in another sense, you are a lot more likely to lose and less likely to win than he is.

To keep the numbers easy, let's pretend for the moment that you're backing him in $11 10-seat SnGs.

Suppose your friend is finishing in each place 10% of the time - that is, breaking even on the prize pool but losing money to the rake. If he plays 10 tourneys, you and he pay $110 ($55 each) in entries. He collects a total of $100 in prizes. He breaks even, pocketing $55, and you lose $10.

If your friend does 10% better than that - ITM 33% instead of 30% of the time - he will collect on average $110, which in the usual sense makes him a "break-even player" -- but will, under your arrangement, result in him making a $5.50 profit and you taking a $5.50 loss.

He has to collect on average $122.22 before your expected share of the winnings comes to $55 (and he pockets ALL the profit.)

There are players good enough to average $130 or $140 back on $11 SnGs. Suppose your friend is such a player, and you expect to split $140 - $77 to him, $63 to you. Your friend made $22, you made $8. Are you satisfied with a deal that will result in your friend making three times as much money as you do in the long run? Were you aware that that "10% difference" you agreed to was, in effect, an agreement to split profits 75-25-ish?

I think the deal you MEANT to offer your friend was "I will cover 50% of your losses and take 45% of your profits" - which is a LOT different from covering 50% of his entry fees and taking 45% of his winnings.