Oh and allowfleeing is a command for when a man is under fire and ways the chances of running or staying where he is. I don't think it is affected by arty. Only by nearby enemies...
Actually, I've noticed that, yes, groups WILL flee when they come under artillery attack, even if they aren't near actual enemy troops.
On second thought, that happened when I was using CoC arty, so they actually WERE being fired upon by real enemies (not camcreated shells); although those enemies were about 2000 meters away...
I don't know if you are using CoC arty, or camcreated arty; that might have some impact on what they do. Try disabling their "target" ai, as that controls their movement during combat. I'm sure putting them in "careless" mode would work as well, but I don't know if you can force them to take their weapons off their backs in that mode.