I have always heard that it doesn't matter what cover you put an AA gun in - it will perform the same against enemy planes. What I did was go to the editor and set up a quick battle in order to test this with some specific units involved. For the Axis side I chose the following:
Here is my Allied side:
I divided the map by a long hill so enemy units could not see one another. I then put thick patches of woods, pines, and scattered trees on each side, along with open space. I distributed the Axis and Allied units about the same in a mirror fashion on each side.
Here is the Axis side setup:
The quad AA guns are circled in red. One is in thick woods, one is in pines, one is in scattered trees, one is out in the open, one is in the open elevated on the hillside, and the northernmost one is in the open, but shielded on the south side by all of the woods. The Somua (in scatterd trees) and Pz IIIJ (in open) are plane bait and are also circled.
Here is what happens on turn #2:
All guns in the open pick up the plane when it is over 1200 meters away. Simultaneously, the Pz III buttons up. Note: the guns in the trees have not picked it up yet. This is important because a gun will not pivot towards the plane and fire until it visually spots the plane. If the gun picks up the plane too late, it will spend all of it's time pivoting and may not get even one shot off. Here is the next pic:
The gun in the woods has finally spotted the plane - at 727 meters. notice the gun in the pines still hasn't seen it. By the time the gun in the pines spots the plane it will be almost overhead or passing by, giving the gun no time to shoot.
Where should AA guns be placed for maximum effect? I would say where they will pick up enemy planes the fastest and have to pivot the least in order to get the most shots in. While doing this test I discovered that out of 17 plane approaches I counted, 14 times the plane came from the friendly side of the line, not the enemy side! So could it be that for maximum protection your AA guns should be out in the open, near the front lines if possible, protected behind a knoll from enemy ground units, pointing backwards?
In my tests with both Russian and German planes I found that they were all spotted at just under 2000 meters by guns in the open. The elevation of the guns on the hillside seemed to make no difference. Guns in the scattered trees picked the planes up at around 1200-1600 meters. Guns in thick woods picked them up at around 200-500 meters, and occasionally never did see the plane. Guns in pines were the worst - they picked up the planes between 150-400 meters and about half the time never spotted anything. The guns at the edge of the woods in the open performed depending on where the plane came from. If the plane came from the clear side it did well but it came from the woods side the gun did poorly.
Guns in the open also continued to track and shoot at the plane as it flew away much farther than the other guns.
If you are curious as to how the senario turned out, I ceasefired after 15 turns. The Germans won because they knocked out two of the three Russian 25mm guns in the open. The Russians did not knock out any quad AA guns although there were three in the open. But I believe they were scared off early by the superior German quad guns. No planes were destroyed on either side, and surprisingly no tanks were destroyed, although one was immobilized. That goes to show you the guns did their job disrupting things.
Another thing to note is four different times there was the sound of a plane going by but no plane was spotted.
Also, POS is right in his thread, cover arcs make no difference - the guns will all still target planes regardless.
Something else of note is planes never came on turn #1 of the quick battle. Perhaps this is on purpose to help protect setup zones?
"Most sorts of diversion in men, children, and other animals, are in imitation of fighting." - Jonathan Swift