[Aeraaa]

I wasn't able to confirm this, but I have the perception that units that overcrowd a hex are more susceptible to artillery effects. With infantry this is a no brainer, but even with armor I witness far more damaged or KOed tanks when there are say 3 of them in a single hex.

Regarding dug-in units, calibers 122mm or greater are the ones more likely to produce casualties (although I do get some odd successes once in a while, f.e. a 25-pounder knocking out a dug-in Panther tank, or an 81mm mortar killing an infantryman). The others are good for morale purposes. Regardless of that, ALWAYS use artillery when assaulting dug-in units, it will make your life much easier (just careful when close to enemy positions and fire is unobserved, friendly fire sucks).