RTS are territorial and the generaly rules for tankmates for them are as follows:
1) Too big to bother (ex. Clown Loach and Oscars)
2) Too mean to mess with (ex. Convict Cichlids)
3) Too fast to catch (ex. rainbows)
I've never kept Angels and so am not very familiar with they're personality.
Also since RTS are more concerned with the ground area of a tank than the height, if you give them a big area to patrol (anything larger then three feet long) and break up lines of sight as much as possible (plants,
driftwood and decorations are great) since it's hard to chase what you can't see.
Best of luck,
Red