Just tested the following:
1v1, Angoville, SU vs OKW. SU using Lend Lease's fuel supply drop.
CheatCommands mod.
OKW starts with 3 flaks as "bunkers", they all fire 18 rounds to the plane before it goes out of its range. Schwerer fires 6 times when put in the middle of the map.
12/31 times were taken down by 3 flaks + schwerer panzer.
5/30 were taken down by 3 flaks (base).
10/30 were taken down by 1 Schwerer HQ.
7/10 were taken down by 1 Schwerer HQ + 1 FHT (2 of those 3 times that didn't, somehow the FHT didn't fire).
Hope this helps.
I still find it stupid that OKW gets AA by sideteching (and thus deny some allies' abilities), specially when they also have AA bunkers.
I did a quick test myself and my supply plane was shot down 0/15 times(!) on Angovile against base AA alone.