The mimic chest is so frustrating. Having it be 11 means it is basically instant death until there are only a few hidden spaces left on the field. There's no way to predict when they'll show up. The only way around it would be to skip over some pretty necessary chests until you're strong enough to risk it.
I agree with this -- the mimic is intended to be an inherently risky monster but with enough information (what's around it) you should be able to tell if its a safe chest or a mimic. It's intended to make you rethink the chest as a perpetually safe tile. It's most deceptive when you unveil it with no surrounding knowledge, that's for sure.