Yeah, you could do 1 door to solve the problem but I think the gameplay would become a bit too predictable. It's fine to have enemies come from any door I think, just as long as its telegraphed. Doesn't even need to be an arcade style "!" which can admittedly be too obvious sometimes. Like the door opening with a bit of light shining in before they come out is enough to telegraph the oncoming enemies with a bit of nuance. making sure the player doesnt find themselves having an enemy spawn on top of them during battle is a problem to solve for sure in any case.