Joyce Wilkerson mentioned keeping a small group of ocellaris together in her book--two were a spawning pair, one acted as a "nursemaid" as Winwood describes, and the fourth was allowed to coexist on the very fringes of the group, but got chased a lot (I hope she eventually removed him). I know one LFS in my area used to have a trio of black ocellaris in their 500G display tank, although they only have a pair now (I'm not sure what happened to the odd man out--I'll have to ask). Definitely not something I'd recommend, but it is very interesting to read about.