I understand that they need open swimming space and quite a lot of room.
I have 4 Bosemani rainbow fish and they seem to spend most of their time swimming very fast in the upper levels. They seem to like charging the filter jets! At the same time, I have a big piece of bog wood and a big rock and lots of plants (the top 1/3 is empty for swimming space) and they seem very curious exploring the holes and nooks and cranies in the wood and diving through the plants.