Is this because I am using the wrong artillery to defend my units? I mainly use the Sturmpanzer along with the 21cm Mrs 18 and the Wurfrahmen 40. 
Also why do artillery units only return fire once when protecting a unit ??? ie allied infantry attacks my infantry unit which has an artillery unit behind it with a range above one - it only fires a protection shot once. Then when another allied unit attacks the same unit again, the artillery unit will not lay down a defensive shot again even though it still has enough ammo. This has annoyed me throughout all the games because artillery units should keep firing until they run out of ammo.
