I think all angels should be kept as pairs, their mood and behavior is much more interesting and natural. It's almost like they don't even realize they're in a tank anymore. The nightly dances are cool to watch.
I have a trio of potter's in my home tank and that was awesome until the medium one started turning into a male. Now the poor guy is miserable and constantly gets chased to his corner. He is also constantly trying to mingle with the female which pisses off the dominant male and throws the whole 'pair' thing out of whack. Every time the dominant male and female start their nightly routine the small male interrupts and chaos breaks loose. Too much tension in the tank now.
Might be best to stay with a pair.