Why don't you attack angels with pixies?
Added 2 minutes later
[del]Okay, I'll say it myself: AOTD triggers on the attacker OR the unit with higher SCS.[/del] No, that's not it, I need to test it a bit more.
Added 4 minutes later
It's strange, I attack a blue hero with angels using pixies - AOTD triggers on the 1st unit, but when attacking from a Necropolis group - it doesn't...