How do you define a "bad beat"?!?
Is it any time you get in as the favourite but still lose? Is it when you're in as an 80% favourite and you lose? 90% favourite?
The amount of times you lose, in the long run, will be the remainder of the cutoff point you choose. If you define a bad beat as any time you're in as a 90% favourite or better and lose, then you'll be losing on a "bad beat" about 10% of the time in the long run.
Thing is, I'm not really sure how this information is helpful.
The thing about STTs is that you will be getting all in a lot. It's the nature of the game. Maybe that makes it seem like you're getting busted on "bad beats" a lot, though I'd be surprised if that was actually the case and not just selective recall. Either way, you're being results oriented and that's the wrong way to go about this.
Focus instead on making the absolute best push-fold decisions you can when it comes to that stage of the game. That's probably the most important part of being a winning STT player.