24 gallons isn't all that "nano". I would consider it "mini", but that's a whole other debate.
I keep a GBTA in a 20 gallon tall with a single clownfish, an arrow crab, a couple of soft corals, 4 hard coral, and a bunch of mushrooms. I have heard that BTA's will get bigger in dimmer light, and stay compact under bright lights. I have 130 watts over my reef, and the anemone seems happy. He does roam around sometimes. It makes it more exciting; every time I go by my tank, I "have to" check it out (as if I weren't checking out my tank anyway just because it's fun to look at) and make sure the BTA isn't encroaching on something I like.