I don't really count the pop door for ventilation. I made the coop the have enough ventilation *above* their heads as you say, for 4 birds. It was supposed to be just right, but then chicken math interfered. There is still enough ventilation for all 6 when there is not excess moisture...but when there is I'm afraid it's not enough. That's when I kinda have to hope the pop door counts for something as well. The "official" vents are up under the overhang of the roof.