you are putting WAY too much logic into it.
dont forget that this has to be increased to deal with people leasing every type of plane in existence. So, we like to think that you have to cross train all of your techs on every plane. Therefore, the more planes the more techs...
Yes, but again, it shouldn't go up "per plane".
If it took $100K to maintain 1 plane it shouldn't take $300K to maintain 2 planes. In reality, it should take, say, $150K -- that's only $75K/plane, so less than the cost to maintain 1.
However, your first statement is true -- you can't put too much thought into the figures in AWS. The numbers are what the numbers are. Do they make sense? More often than not, no. They're averages of averages to begin with and you tack on game design decisions on top of that and who knows what's really gonna happen when you do something. You just make note of it for future games and go with it.
Does it make sense that all your planes become twice as expensive to maintain when you add a new fleet type? Nope. But it's what happens here. Does it make sense for every base to increase your overhead salary by some 25-30% -- hiring thousands of employees at HQ just because a base was opened? Of course not. But in happens here. For game balance purposes many things happen here that don't necessarily make sense or match reality.