Damned if I remember anymore, but I think it was attack.
If not that, then magic. No other candidates.
The DoT might just easily hit its damage cap of some <=10% of target's max health per tick though.
Late edit: Rather than just attack, weapons probably play a part in it too. Just can't recall if it's the melee or ranged slot.
If at first try it doesn't explode, it ain't Jack who wrote the code.