...and not getting very far.
At first, I thought the chance of an escort appearing was connected to a percentage chance for an escort happening. However, this doesn't seem to be true. I set up the AM_AirSuperority mission to appear very early on (when the ticker hits 10, or 3 game days in) and fiddled with various escort chance settings, from 10 to 1000, and it didn't matter what it was set to, no escorts would appear. Thinking it might be that escorts can only appear after a given boundary, I then set AM_AirSuperiority to appear later (100), and played through for a game month. No escorts appeared. For the same reasons, the escort chance isn't linked to the ticker, either.
I'm currently looking to see if the escort chance is linked to the players' score, perhaps escorts can only appear when the player has accumulated enough points. I'll get back to you on that. However, I did find out that the AirSuperiority mission is only initally triggered when you shoot down your first aircraft. So... that's something!