For 9,9, I eventually just figured out a reasoning for it that made sense: Basically assume that you and the dealer get tens on all draws. For 2-6, you're playing the dealer's bust, so put more money on the table. For 7, you're assuming that the dealer will get a 17, so keep the 18 to lock in the win. vs 8 or 9, you are again trying to either tie or beat dealers 18 and 19. And with dealer 10 or A, you're going to lose, so don't bother.