Yeah, they were fighting. Since you only have 2 in a small tank, I'd say they were fighting over dominance. Even though they seem to have stopped, I'd expect it to get worse. If it hasn't happened already, one will eventually establish dominance. After that, the loser's life will be made miserable until it eventually dies.
I had 2 angels in a 55 community tank with plenty of plants. One of them became the dominant one after a lip-locking incident. After that, it went downhill for the loser. He was constantly harrassed. He would always hide in the plants, usually in whatever position he landed in after a panicked retreat from the dominant angel. He'd only come out to feed and then be quickly chased back into the plants. Eventually, he got so stressed that he began to lose color. His fins even began to erode. I took him out and fixed him up in a quarantine tank. He seems to be a little larger than the dominant angel now so I'm going to try and reintroduce him. If that doesn't work, I'll have to trade him in to the LFS.
Anyway, IME, the behavior you've seen will most likely get worse with time. I would get a larger tank ASAP or you'll probably lose an angel. You really need a bigger tank anyway. Your angels will also need something larger than a 20 gallon.