Movement of ground AA unit blocked by enemy a/c

[PoorOldSpike]

I wanted the Mosquito fighter-bomber to attack the SP artillery under the Bf 110 but all I could

I just ran a test and the Mosquito FB could only attack the 110 like you said, but then I attacked with a Battle bomber and it bombed the SPA after it shunted the 110 out of the way.
Conclusion- only bombers can attack ground units underneath an enemy plane but fighters and fighter-bombers can't.
Unless somebody knows a magic key combo to make them do it..