I think the problem partially involves harems and females changing into males. According to Scott Michael, all males start life as females and the social situation dictates the change (see his enchanting book Angelfishes and Butterflyfishes, pg 221). You can find this idea via ai or, but Michael's book is still better ;). So if you get a single male and some females, then there is no male on male competition. Bigger fish are more likely to be males (and some species you can tell the difference, but it is hard for others). I kept 3 dwarf angels in a 120 for a while (CB, flame, pygmy). When the flame passed, the CB became more colorful. Perhaps changed into a male? Lots of hiding places helps and ensuring that everyone can find food helps as well. Currently, I have 4 dwarf angels in my 180 (CB, flame, pygmy, and flameback), but I got them all small, added them together, and prefer lots of fish hiding places to optimizing for flow. My CB is certainly the largest. I've had the flame for a year or two and it is still fairly small. Matches the idea that the flame is a female that is being kept from transitioning by the CB male. Also, I have read that if dwarf angels are by themselves for a while, they change to male and can't go back. And species matter too, with some more species being aggressive than others. And of course, in tight enough quarters females may compete, but perhaps to a lesser degree than males. Perhaps a similar problem to anthias groups. Just my two cents.