As for artillery maybe it would be best to simply add supply wagons for artillery and also to force the ammo features onto artillery, currently you get artillery only out of ammo when you isolate them even when no artillery ammo is left. When it works for them like it works for infantry & cavalry maybe that would solve some problems.
Besides that there could be a random chance that captured artillery is on low or out of ammo as the wagons with the ammunition may have escaped.
And with these artillery supply wagons you could allow the captured unit to be moved coasting x supply to make the captured artillery mobile again, so we would finally be done with the problem of forcing units to stay with captured artillery to get the victory points.
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Lieutenant General Christian Hecht
Commander I Corps, Army of the Potomac
"Where to stop? I don't know. At Hell, I expect."