I don't understand Farber, that's plenty of room. You don't have to remain over the red patch. On RAF we are always having to fly inland and circle whilst climbing - is the 109 turning circle that bad?!?
There are also a ton of airfields in this territory so you don't need custom ones. Besides, you need a smaller area because you have no radar and you would need to be able to have a chance of spotting the incoming raid.
Would you like us to make this map? We had already planned something similar for our own campaign, it would mean German ground forces being supplied and a British raid on a bridge behind the lines, or a raid on your advancing troops, which the RAF would escort.