I think a 29 for a single angelfish is acceptable, although not great. The real problem is when the angelfish grows out and decides he doesn't like his tank mates anymore. I have a 29 with a female Angelfish by herself because she does not like any company.
She is very aggressive and even killed a mystery snail that was in the tank. She spends her days attacking the air bubbles and occasionally laying her eggs and eating them. I don't think she's unhappy or cramped, although I may upgrade her to a 37 since it will fit on the same stand and be a lot deeper.