From my experience, whenever a model(or part of model) is on the parking area, you cant spawn there. It doesnt matter, where you have your center of the model.
Have you ever tried the cirrus cloud mod? Even if the center of the model is around 20 km from the airbase, you cant spawn there, because the huge flat model is above the airfield.
If you can fix this, that would be realy great.

Ells, interesting idea to get rid of the collision model. I will give it some tests.
EDIT:
I just remember. It must be possible somehow. I remember seeing the on the ramp, in their hangars. I wonder, if they spawn in those right away or if they spawned somewhere else and taxied into these hangars... PSV, maybe some hint?
