I transfered a decora from my old tank to my current 240 and then three months later added 2 more, in the first week they spread to different spots in the tank but then joined together and now hang out generally in the same area in the center of the tank.
aprox. a month later i added 4 regular firefish and they did split up to two pairs that spread to the 2 opposite ens of the tank, but while the pair on the right side is constantly out swimming in the open the pair on the left mostly stay in their large cave and come out only from time to time when i feed the tank.