million gross ND brings in. I'd make that 5 points fixed no matter what the gross revenue evolves into. The theory is "you win, the business grows, the top line grows, your 5 points becomes $5 million, $6 million, $7 million, etc."
In short, there is no upper limit on what he can earn at ND because that 90 can double or more over 10 years if we are cranking out titles -- at least that would be my sales pitch.
EDIT: I'd also point out that the 62k * 4 = 248k per kid that goes to ND, the use of jets, properties, etc. also probably adds up to about $2 million more over four years.