My BTAs all did well. I have had two GBTAs and one watermellon.
I added them to a place in the tank that had a crevice, preferably vertacle, with medium flow and access to light. They all hid, but after a few days they would start to send out tentacles. I would feed these before they really started moving around the tank and they all stayed put until I moved them.
The BTA is looking for certain things and if you supply them, they should have little motivation to move. Those things are a nice firm crevice to plant their foot inside. They can extend as much as they want to receive light. They also want medium flow and food. When all those conditions are met, they should have little motivation to want to leave. Considering the amount of energy needed to move.
When they do plant themselves and remain in a place for a while, I would stop feeding them. If you keep feeding they will expand to a size that threatens all the nearby coral. I fed mine fresh shrimp and they would rarely excrete. Some people feed silversides, but I think they excrete more on that diet. They will also pull food from the water when you feed the tank.
Good Luck,