I'm not gonna say it would be okay because Cichlid tanks are an ever-changing playground. But I can tell you that I have kept a 2.5" Cichlid with my 6"-8" Cichlids before with no problems. The little guy posed no threat to the bigger fish so they left him alone. Just provide lots of rocks and driftwood to break up line of sight. From my experience, adding similar sized fish (i.e. large fish with large fish) usually triggers aggression as the new fish is a potential threat to the established hierarchy.