I have a 5" Nandus Nandus, I got him last May and he was 4-4 1/2".
If you can provide the right setup, they will feel comfortable and be somewhat active. When I had him in a 20g with a 5" raph, he would change spots quite often and hide where he was very visible to the viewer. When I put him in other tanks, and the setup wasn't right he would hide a lot better.
As for frozen, I really wouldn't count on it. In order to get fish on frozen, they generally need to be sure that you feed them and are no threat at all. Most fish that are on frozen, snatch up the food so fast, they don't even realize that it wasn't alive.
Try subdued lighting, and get them hungry and try feeding them freshly dead rosys. They may jump up and eat them before they realize that they are not alive. Current in the tank always helps with this as well.
Mine also hates noisy tanks. He seems to come out and swim around when I shut off the old noisy aquaclear filter during water changes. He seems to not care so much about my presence.
They are cool fish though. I wanted to try to get a small group of them, but one died right after I got it, and another wedged itself into a piece of driftwood that I took out and died, so I just have the original guy.