odd, I always though that africans were meaner and more aggressive pound for pound, or is it ounce for ounce in this case?, and that they could shred larger americans assuming they weren't lunch sized to them.
The reason most people do not mix African and CA/SA chiclids is they have different food and water parameters to flourious. Africans do best with a PH of 7.2 to 8.0 or higher even. While the CA/SA do best in a PH near 6.0. Protien levels are different and if you feed an African food higher then 45% protien your risking them getting Bloat. Not saying it has not or can not be done but is not the best conditions for the fish to thrive.