BTDT, the problem stemmed from someone introducing a recently neutered male with a super dominant predisposition to another passive but large male and the subsequent response was very poor and essentially fixed permanently only to that pair.
That lack of foresight on someones part scotched the possibilities of a proper result for those two.
Some things cant be fixed, and the only real potential for a good outcome was not to let a bad response be learned in the first place.
I had to jump on them more than once when someone would break the two closed doors separation rule. IT did improve to the point that I could keep them apart without the blankey but not with any confidence of being safe and unhurt myself.
That never got resolved until one was removed.