From my experience, the retaliation damage from Power Guard is considered to be that minimum of 1 damage needed to get EXP that way.
However, I also remember that while this 1 damage deal will give you a share of the EXP, you don't get that much unless you land the killing blow on the monster. My experience with this is from PG landing killing blows because the monster had only 1 HP left, usually from a mage spamming poison mist on a map who happened to have forgotten to kill a few monsters. I got around ~300-500 EXP for PG bumping into Spirit Vikings while they had only 1 HP left.
Bookmarks