The bigger the tank, and the lower the population density, the better the chances of compatibility. When they gotta compete for space, it's an equation for wars with humans, fish aren't that much different in this area.
I decided to try moving my Apistogramma Agassizi.
They went from a 29 gallon tank with Rams they couldn't get along with to a 10 gallon by them selves. Well that solved the agression problem, but I was back to a species only tank. So I decided to put my Apistogramma Agassizi in my husbands 75 gallon tank. The 75 gallon has about 27 Barbs ( mix of Tiger barbs, golden barbs, green barbs, and black barbs), a six inch Red Tailed Black shark, and a Marble Sailfin Pleco. They seem to like it. I think the male is actually happier now that he has smaller fish to boss around. So I guess the size of the tank really does make a difference with these fish.