Trying to reply to my question I found this Lee's interesting statement on Consimworld forum:
I feel moved to make a necessary change to the way we model Gebietsnachtjagd in the game. The change is, if anything, a great simplification and will eliminate some of the abuse we have been seeing. It would confine single-engined units to more historical behaviour. It does, however, involve some changes to the map for the Downfall scenario to recreate I NJG11's hunting zones over the Ruhr...
I'm starting to assume that hex I9 of the Downfall scenario map should be shifted from 7.Jagddivision to 3.Jagddivision (together with the I NJG11's airfield).
Or I NJG11's airfield itself should be shifted to one of 3.Jagddivision hexes.
This could enable I NJG11 to activate I6, I7, I8 Himmelbett hexes and make Mosquito Hunting attacks as described in 9.3.1 Gebietsnachtjagd rule.