I put a good crowd into a 240. Started with 30 or so all under 6". I have wittled it down to 20. I have 6 Syns, 2 briedohri, 2 gt, 2 festae, 1 female nic. 2 crysti 8"(African), 1 tyrannochromis 11"(african) 1 red severem, and I am taking out 1 trimac and replacing him with a argentea.
But I think my success is due largely to them being juveniles and growing up together. Now the syns are 8"-12" and they are some what of a melow group.
I think it would be alot harder to throw a bunch of almost adult ca/sa's together in a tank, but you never know??
Neutrino is right, its alot about the species and individual fish. Do alot of research and be patient. To summarize I would say crowded is better than scarce..?