electric yellows don't get too big,
i might suggest, get four of them and 1 male three female souliosi, or about four more rusty cicglids to make a great ank these fish are less agrisive and should do well in a smaller less sgresive tank with the electric yellows there is information on all three of these fish in the fish index
Edit there are still amny other options i can't think of them right now, you could try pseodotropheus scofoli if you want something more agresive i would expect it to work