Good to know (that the only thing that matters is money, and the gorgraphical regions are irrelevant).
I was wondering though: Let's say I have a plan 3c from your list. The option is the same (permanent) but the amount goes up week after week. What makes it go up? It seems somehow related to the size of the company, but what in particular?
# of cities serverd?
# of routes?
# of passengers?
It scales according to the number of origin-destination pairs that you're flying. The more destinations you fly to, the more locations that now need to be advertised in. The number of flights themselves also seems to have some increase as well (particularly notable earlier in a game), but the effect is a fraction of that of flying to more destinations. It also, as all expenses are, is effected by inflation, so it'll increase slightly all the time.
That's why Regionals get hit SO hard on CI expense -- because they have so many OD pairs, many of which are generating only very little money. And that's why sticking to fewer, denser routes is a great way to minimize your expenses.
It also steps, it's not linear. So, you add routes and add routes and it doesn't go up. Then you add one more route and it shoots WAY up, sometimes a few million a week, which can be killer for some airlines. So you thought you were making a ton, then suddenly that last route you added cost you a ton
of money. In reality, that should have been spread over all the other routes you added, but the expense just doesn't go up until you hit a certain number of routes (don't know what those numbers are).