This doesn't obviously have anything to do with the scenery.
The scenery can't do anything more than simply defining the correct parking stands. But the amount of traffic generated, which might cause congestion, resulting in delays, it's only dependent by the AI Traffic product you use, and their schedule.
Yes, ground vehicles can affect it too, because they might cause further blocks so, either you adjust your AI density down, or you adjust the ground vehicles density down, or a combination of the two, until you solve the congestions.
