4 sq ft is just the easiest general rule to go by. Some birds are fine with less. Some flocks need more than that. So averaging it out is a convenient way to get a rough calculation for numbers.
Not sure on the door... never tested that! It's more the location that they memorize. When I transferred my hens from an old coop to a new one (within the same run), I locked them in the new coop for 2 or 3 days, and when they came out the old coop had been removed. 2 of 3 hens still went to the location of the old coop and sat down on the ground at dusk, right there in the middle of the run, as if the coop would somehow materialize around them.