It was turn 60 when the first air attack happened. Then on the very next turn, I killed the spotters. So it wasn't a setup phase fire mission. Around turn 75 was when they called in the second fire mission over a KM away from the initial fire mission.
I think you might have hit the nail on the head here. The past few times I've attempted this mission, Russian air support always comes at turn 60 so I believe it is a pre-scripted fire mission. It's just not in the same place every time. If the Russians have visual on any of my units, the fire mission gets called on them, but if they have no visual on my units, it seems to always default to my deployment zone. The thing that is still weird though is the fact that if this was a pre-planned mission with the details manually worked out by the scenario designer, why would the fire mission jump around from different locations as if it was a live non-scripted fire mission? Is it possible to script fire missions that target spotted units, but also default to a specific location if no units are spotted? Because that would explain everything there.
Also it might be the second case you described where I might have killed them on the very turn they called the mission, but then that would mean their air support takes over 15 minutes to arrive which seems too long. Then again, I've never played as Russia yet so I don't know if 15 mins for air support to arrive is normal on Iron difficulty. I would assume the average is like 10 minutes.
Ultimately though, I think its safe to say its not a game issue, but just how this particular mission is put together. I've also never experienced this issue on any other mission so I'm thinking the designer has some funky things going on with the Russian air assets. I've never really messed around too much in the editor so I don't really know what it's fully capable of doing, especially with fire missions, but your response definitely is pushing me in the right direction. One of these days, I need to find a way to open this mission in the editor to see what exactly is going on.