I was away from this fun for 30 years and one of the first fish I added was a Flame Angel. My new system is way larger than a 40 so I cannot comment on that but the personality of this little guy is off the charts.
When I placed him in the tank he only hid in the rocks for about 30 minutes. Then he began running all around the tank running back and forth in between all the tunnels until he found the purple tang the same size.
The Tang was added 4 days earlier but only hid in the rocks. Once the two found each other the Flame convinced him it was fun to run around the tank.
It is now a few weeks later and I have 8 very different fish. They all get along and are mostly out in the open. The Flame is definitely the leader of the tank.
When I drop a frozen food cube into the tank the Flame and the Tang go there before it even thaws and are the first to start eating.
So far no one picks at the corals I have but they do rub against them and cause them to close for a while.