Units specialized on defence/ambush

[Mowgli]

As I'm delving deeper into the game thanks to the exciting PBEM battles I'm having with larsonney, my overall positive impression of the game grows and intensifies. 

But the way some units can be used seems a bit strange to me. I'm not saying that they're overpowered per se, just that the way in which they work seems implausible to me. I'm talking about units that are supposed to excel defensively: anti tank guns, larger calibre flaks. Basically most units that need to be towed. Perhaps even including - to a minor degree - self propelled anti tank guns. 

What strikes me as odd is that these units are very effective if you let them fire "offensively" (in their player's turn). This leads to situations in which a stationary unit of 88 flaks fires at a unit of tanks which is positioned in a village and knocks out 3 tanks. This can happen round after round, unless you move the tanks out of the flaks's sight. As flak units can come in huge sizes, share the Germans' high morale and their defence is not that bad, it's usually a better idea for the tanks to retreat from the flaks. So in a way, these flaks work very similar to tanks with a low armor but superb guns.

I think it would be more realistic and immersive if these defensive units had their overall hard fire values lowered a lot and instead gained a big bonus on their opportunity (="defensive") hard fire. This would really make them excel in a defensive role and incite players to use them in more plausible ways (e.g. sp. AT guns firing at an approaching enemy, retreating in their own turn). If you approached them or fired on these units, you'd need to be prepared to receive very strong return fire. So basically, these units would have a bigger "stand off" effect. In the example above, the tanks could stay in the village, but at the same time, attacking or moving out of the village would be very dangerous for the tanks.

Any opinions on this topic?