I noticed that when you have units near your ACU with restoration field (tested only with level 2), units don't get its benefit as soon as they get a veterancy level, which will replace the restoration field regen rate. Only if the units leave the Restoration field effect zone and come back can they get the proper regen rate again.
This behaviour prevents any offensive use of the upgrade on the battlefield. If you choose to help your Ilshavoh to remain alive with the upgrade, it'll be a pain in the ass to actually take advantage of the upgrade, with lots of babystting. If your Ilshavohs kill stuff, they lose the benefit of the upgrade, unless you make your ACU retreat, then walk near the Ilshavoh and check if each one gets the proper high regen rate. And since the AOE is so tiny and unclear, well it's like completely uneffective in the heat of battle.
This behaviour makes the upgrade utter garbage, not only because of the cost of the upgrade for such a tiny AOE but also as far as gameplay goes. Can it be fixed so that veterancy regen stack with resto field? I thought it was fixed but apparently it's not.