My friend had luck with smaller clown triggers by slowing the flow in his tank. He removed the one of two Koralia 4 for a months then putting the Koralia 4 back in. This was in a 210 also.
He said when he had his first one in the tank the extra flow kept him hiding in the rocks. It wouldn't come out to eat or swim and ended up dying. The second one he noticed the same behavior and then slowed the water flow. With in a few hours it came out a little bit. After a month it was swimming around like nothing.
The little "baby", yellow nosed CTs are very hard to acclimate and have a poor record surviving. Get one past the yellow nose state and they're easy. You seem well aware of the CTs reputation and its well deserved. they can go postal at any time...fascinating fish though.