Very good question - and you are basically right.And here's another noob question, I understand wht you'd take away the left over 2 yellows, becuase of the agression, but then why is it cool if you added the comp? I've read that it can be a color thing, as in the aggressors will be more aggressive towards those that are the same color as them. Is that why a comp would work? It doesn't look like he'd be a bigger badder fish or anything obvious like that.
Firstly you have color as an issue - in africans it will almost always be higher between conspecifics (fish that look like one another) of the same gender especially males, when the fish are sexually mature - shown by pair forming in leilupi.
Secondly, the leilupi do occupy a little bit different zone in the tank, being largely closer to the bottom. The Comp will be happy to bumble around all over, although like all cichlids tending towards the bottom third.
Thirdly, the leilupi will probably chase at the Comp if spawning/fry but the Comp should be big enough not to get too stressed out by this and the leilupi not so aggro that the chasing is persistent or fatal (the size diff helps here too).
Bear in mind stocking cichlids is always a bit hit and miss and a lot comes down to individual personality (partly why they are such great fish). It hels to have a plan B (rehome, return to LFS, new tank) for a fish that is not working out.