[DRG]

1/ They are obviously not moving so not taking a penalty for doing so....

2/ You have to get close in forest and smoke and they (usually ) get the first shot in and because it's one hex range the effect is higher

3. you have now learned that just because it's immobilized does NOT mean it's helpless. From your description I can just imagine what transpired as you assumed an easy kill then sent in tanks piecemeal and they were chewed up.... never assume a wounded animal is helpless...same for disabled tanks in places where you have to get up close and personal.....that is what the infantry is for AFTER saturating the area with artillery