I don't know what ACE is...but perhaps using kennel crops, or an herbal calming spray (check a good pet store) might be added if you want to try reducing the meds. He and you have been through a LOT - and he might be stressed enough that he thinks his tail needs to be attacked - kind of like PTSD.

Check with your vet about these items - even though they are not drugs, as such, they might interact with the ones he is taking.

HUGS and prayers for you and dear Maxx.