I've played through 3 times with the stealth character and this ability has never worked for me or the opponent. I've pushed it to >30% each time and tried quite often. I could just be unlucky, but it seems it's not working.

Same here. I had it up to %40 and failed every time.

I, personally, haven't tried the ability because it didn't seem very useful... but it might be one of those things that they're hashing out.

Regardless, thanks for the post.