Explosive Arrow damage, as far as I know, is not Magical. It is not boosted by any stats. That is why Splitting Arrows is almost always a better Area of Attack skill. It will be boosted by Dexterity if Dex Ranger, or Intelligence if Int Ranger. Plus weapon damage too.
So what does boost Explosive Arrow at all?
Ranger Strength?
Way of the Ranger?
Anything else?