Right now, all airfields are are "average" targets. If you want to totally eliminate Axis airfield attacks and other bomb attacks in TitE, there is one thing you can do and it only costs 1EP+1PP. Build 1 Flak Unit and you basically eliminated the entire air aspect for the Axis FOR THE GAME.
If you do the probability calculations, you will find that it is a net negative for the Germans to bomb airfields or bases with that "1 damaged aircraft per turn." You have better odds just flying your missions with escorts against inferior (for a time) enemy fighters. So on turn 1 for Soviets, 1 PP and 1 EP is an easy spend. Heck, you can spend 2PP and 2EP and really send it over the top. You'll never need to spend any more!!! (No need to buy 6 Flak)
The reason this part of TitE becomes "broken" for the Axis is that there is not an abundance of German aircraft. I encouraged all TitE-ers to use this method. However, I don't think the intent was to stop airfield bombing by building a single Flak unit, but that is basically what it does.
Now, I had a proposal for this a while back on CSW, and it still seems appropriate. We already have a special rule for Hindered Air Forces. So we just need to add the line, "Hindered Airfields are "soft" targets." DONE! No other rules needed and fits right in.
The game logic is that "hindered" air forces are just crappy ground crews ... so these crews just don't know how to store ammo safely, disperse the planes while parked, etc. That is why "hindered" airfields are "soft" targets.
The other nations can maintain their "average" status. And these nations may actually build more than 1 Flak unit to protect their assets, maybe even build 3 or 4 ... now that is an aspect of TitE I'd like to see utilized. Kind of just lame to constantly use air for CAS only since that is the only thing the Axis may gain something from.