a kinda guestimate for telling pairs is if they are grooming each other kinda like picking at each other, the female will aggressively do this to the male. If you want to encourage angels to pair up sometimes clearing a flat piece of slate completely off and warming the tank around 82 will get them in the mood....
29g Tetra Tank
100g Planted Angel/Clown Loach
I can't spell...Im an engineer, I do math