yea it’s too hard to work with the high lip of a pot. A large fajita plate is awesome as it’s easy to get under the fish. And fish is so delicate you don’t want to be coming at it on much of an angle.
I have a 1/4" piece of sheet steel I put on my BGE and leave the lid and vent wide open. It'll get 750 degrees which is more than hot enough and works fine. I've had better results using an upsdie down cast iron pan on a crawfish burner at much lower temps. 600 or so I'd bet.