I was just playing about making a few custom scenarios to try a few things out.
And I discovered that a unit won't fire at another unit, if it mathematicaly can't kill it.
For example, I put a single M1 tank, facing 12 T-62s fairly close to each other. The single M1 fired and killed all the T-62s without them bothering to return a single shot.
It seems to me that even though a T-62 can't kill an M1 on paper, there's still a chance of a fluke shot, or maybe breaking a sight, a track or at least making the commander close the hatch and lose some visiblity. I don't think the T-62ers would just sit there and die.
I mean fluke shots do happen. I remember reading about a british tank armed with a 57mm gun fired at a tiger tank from the front. On paper there is zero chance a 57mm could kill a tiger, yet the 57mm shell grazed off the bottom of the gun barrel, flew straight into the turret ring and jammed the turret from turning. The tiger crew paniced and abandoned their tank. That'd count as a kill surely?