It will be after the next update, I think, since this is one of the issues the update addresses - 'basing' of longer range artillery. I'm not sure how attaching batteries at a lower level would affect things presently (or, indeed, after the update). Be interested to know. Experiment and let us know!
I know that I regularly see the AI properly basing Bn mortars, for example, back but within bombardment range, then using them to support attacks, but these are units where I haven't attached them elsewhere.
Under present code (prior to the shortly-coming update) then for an Attack order basing should happen, I believe, which means the HQ and support units (I assume including your attached Div arty) should base back from the attack and I would hope the AI will take into account min range when doing this. Not certain though. Be interesting to know, as I said. For a Move order, or almost any other non-Attack order, there isn't presently any basing code, I think. So if you attach Div arty to a Bn or Brigade and then give the HQ a Move order you would be in danger of seeing the arty leading the road queue. But that's what the update will address.
