My assumption is that whoever coded this ring didn't realize there were elemental dark and light (noctohelix and luminohelix) spells when the ring was created, and therefore only applied the buff to the other 6 elements. Ideally this issue would be fixed at some point for everything that it affects (elemental spells and evidently elemental siphon) but for the purpose of this thread, I'm only concerned with the devs fixing the inconsistent behavior of this ring for elemental siphon.