Unfortunately none of them 'stay' small. Bubbles, and sebae are usually not particularly fast growers, but I have seen a rose bubble that took up 3/4 of an oceanic 30g cube.
Anemones really aren't that great a candidate for nanos, because they may wander around looking for that sweet spot of just enough current, and high light.
Bubbles tend to wander more than most of the others, but all of them can. In the process they can sting corals, polyps, etc...
There's also more of a possibility of losing fish to an anemone in a smaller tank, just because there isn't as much room for the fish to avoid them.
How old is your tank? Most anemones are pretty delicate, and have specific lighting/flow needs. On top of that unless a tank is 'mature', which basically means it has lots of microfauna and has been stable chemically, for many months anemones tend to die pretty quickly. They need a lot of light, moderate flow, and very, very stable parameters.
B
