ICM and minimal edges

[Isura]

With respect to ICM, what % edge (% equity of total prize pool) do you guys consider a minimal edge in these push/fold decisions? Is a 0.2% edge too small to risk your whole stack or a large chunk of it at the 22s, since the other players play so badly anyways? I know this is a vague question, and depends on a lot of things. I'm particularily interested in those situations on the bubble (or one away from it), where it's slightly +EV to push close to any 2 against a certain range, but if that range changes only a bit (say adding two overcard hands like KJ,AT), a play turns from slightly +EV to significantly -EV. The difficulty I find with ICM is that during the game, the calling ranges change so dramatically at the lower buyins from hand to hand. I often find myself in a situation where I think it's a good push, then realize that my image is lagish or I've shown down some crap earlier, so the calling ranges are not what I expect. I'd like to hear others opinions on what constitutes a small edge vs a big edge in a sng (strictly regarding push/fold decisions when we're open pushing).