I have a flame and coral beauty (( along with a multicolored )) in my 65, put the flame in that tank in August (( moved it from another tank of mine )). The coral beauty and multicolor had been together for about a year at that point.
When I moved the flame, I put it in an acclimation box for a week -- so all could get used to each other -- and then released it. There was some chasing at first, but the flame has established itself as the leader. Haven't had any issues since that first week.