I have saulosi, I know they are a smaller species.
I know alot of people have fit them in smaller tanks.
But I just believe all mbuna should have at least 36". Length matters more than height with malawis there fast fish and like to swim, they would appreciate the room.
In my experience almost all the ones I have seen have grown to 4-5 inches, but a bigger tank and better diet is probably why like mokujin mentioned.