@Reise: Thank you that helps a lot. It never occured to me to use the mission editor ..
I think I will settle for 1000km, and wait at the same time for more user reports. Of course one could parse all airbase files (and check for plane types), but in the end isn't it more important to know the maximum area in the range of long range planes? Under the assumption the enemy
could have them on any airfield? Especially as this is meant to give an intelligence report, not godlike information.
Compare now with the same area in TatukGIS, it seems the 1000 km radii I was experimenting with were spot on already!