1. Assuming he doesn't bluff his air, he only calls/raises with better or folds worse. No mistakes.
2. He can make mistakes and fold better or call with worse.

I am not sure I see how it ties in with your original question though. You already said that we are behind his calling range. So the only way we can gain by betting is by folding some of the better hands in his range when we bet, but then we can't really call that a value bet, it's more of a bluff isn't it?