It's not so much a different strategy. It's the exact same strategy as the 12, you just have to basically not get killed in the first room. The more insane you go in the first room (you need to kill all 6 zombies without dying or losing more than a few frames) the more likely it is 11 as oppose to 12.
Cool! Managed to untie 11 in a game where I never thought that I'd be any good. I hope this one stays for a while, plus I think 11 is maxed so this is hopefully forever the highscore...