Is there any way for a high-level toon to "powerlevel" low level toons?

[nodoze]

Any boosting has to be done open world from my testing. Even if you leave the group while in the dungeon everyone in the dungeon gets split XP. I've been boosting my friend open world and I've gotten him 150-200k xp/hour from lvl 45 to 55. He uses oils and dynamite to tag since he's a rogue while I round everything up with demo shout. After he tags I AOE with mages and warlock.

If you want to be able to help kill the mobs on your 60s the mob has to be not a skull for them and at least green for you (48+ at lvl 60) else all you can do is tank with non hitting abilities and heal outside group

Is it correct that mobs which are marked as a skull to you are exactly 10 levels higher if you haven't reached cap yet?

If that is accurate then does that mean a level 48 mob would be a skull to a level 38 character but not a skull (just red) to a level 39 character?

So does that mean if your level 60 character(s) find a HyperSpawn of level 48 green mobs they can boost any level 39 or higher character with full/regular XP in the open world (assuming the 39 character gets the tags)?