Well as far as I know, the footprint of a 20 tall is like the size of a 10 norm...is it not?
Ive got very little knowledge when it comes to angels, my dad kept them when i was alot younger so i didnt know anything but the fact that they were kept in a 20 gal norm, and about 4-5 of them.
A tall tank is good for angels, as those are tall fish. It's normal to advice a 20 gl. tank as minimum for angels. 2 can be housed in a 20, but not even 1 can bu housed in a smaller tank.
Cories will stay on the bottom, so they will not interfere with the angels.
Go ahead and tell us how things do. If yo are adding fish, remeber to do it slowly to allow your biofilter to catch up.
Moonman is correct. A 20g tall is just fine for a pair.
Personally, however, I'd rather have a larger tank. A 60g cube tank (24"X24"X24") is near perfect for a fully grown adult pair. I'm thinking about getting one, myself.
ummmm, maybe to breed them in and pull them but not longterm. Angels can get really big, I've seen them close to a foot with fins and all, they'd barely be able to move in a 20 gallon. Kyle