AA XP Calculations vs Regular XP Calculations

It's literally been 7 or so years since I tried to level up a new character, beyond just keeping up with the 5-level bumps for new expansion. But recently I have started a new Necromancer and I'm powerleveling him with my higher level characters. So far it's been amazingly easy. I now have my Necro at level 67 after just a few days of work, but I ran into a problem I didn't expect. Since it's been so long since I tried to do this, I'm not that fluent in exactly how it works, so I thought I'd see if someone can explain it to me.
When grouped with my level 85 Paladin, the Necro gets good XP. I go into zones where the Paladin can lay waste, the Necro doesn't do much but stand to the side and snare or nuke once in a while, but my Paladin does all the work and the XP flows in. However, at level 65 I decided to hold up on level progression and switch to AAs for a while and wrack up a few hundred AAs before moving on. I'm not in any big rush and level 65 seemed like a good place to hold up for a while and get AAs. However, no AA XP came. None. Not even a tick. My Paladin is slaying mobs right and left and they are all grey or green to him, but dark blue or white to the level 65 Necromancer, but no AA XP at all. None. Zero. Zilch. I don't mean just bad AA XP. I mean NONE!
So I swapped back to regular XP and once again it flowed in quite nicely and he's now level 67 and will be level 70 soon.
Can someone explain the AA XP calculation and how it differs from regular XP? That way I know where I can stop the regular XP and switch to AAs and make it work.
Thanks.
When grouped with my level 85 Paladin, the Necro gets good XP. I go into zones where the Paladin can lay waste, the Necro doesn't do much but stand to the side and snare or nuke once in a while, but my Paladin does all the work and the XP flows in. However, at level 65 I decided to hold up on level progression and switch to AAs for a while and wrack up a few hundred AAs before moving on. I'm not in any big rush and level 65 seemed like a good place to hold up for a while and get AAs. However, no AA XP came. None. Not even a tick. My Paladin is slaying mobs right and left and they are all grey or green to him, but dark blue or white to the level 65 Necromancer, but no AA XP at all. None. Zero. Zilch. I don't mean just bad AA XP. I mean NONE!
So I swapped back to regular XP and once again it flowed in quite nicely and he's now level 67 and will be level 70 soon.
Can someone explain the AA XP calculation and how it differs from regular XP? That way I know where I can stop the regular XP and switch to AAs and make it work.
Thanks.