Dear Adam, for the Monthly Duel tiers all games are considered - even those that (for some reason or other) you don't play. So trying for the 70% wins means you need (in a month with 30 days) 70% wins on 450 games, this is 326. It doesn't matter if you lose a game, tie a game or even don't play a game - you only get credit for an effective win.
_________________________
I dreamt of spending a day riding a stallion. It was a nightmare.