I do not have experiencies in real war (except as a child during WW2 in air-raid shelter) but I suppose that in those conditions AA guns were placed either on the roof or on the garret and on the ceiling an opening were teared large enough so that the gan will have shooting arc nearly as large as on an open place.
I was too lazy to experiment with SPMBT and I though that the gentlemen here could give me an answer outright
