In mists of old and days long past, there was an article in the Daily Content entitled
Tank-Killing Artillery. It addressed the often historical event of artillery fire breaking up armored attacks. I never used that variant because I didn't think it really simulated the event. I don't think anything really does in this system really does. Still I got to musing about it. The dichotomy of the problem is, bigger shells hitting a vehicle, or near it, are more likely to cause damage. Conversely, bigger shells come in smaller numbers, thus less likely to hit. In other words bigger results at diminishing returns.
The idea that eventually formed was getting a die roll for each each X result times the number of batteries. This creates a push-box effect of wanting more, smaller batteries because because you get more dice on an X, verses wanting a big batteries with are more likely to get that X in the first place. The effect on the game is likely to be small, but I think it is worth trying sometime.
P.S. Never formally adopt a house rule, before testing it at least 3 times.