Now that's interesting, I would never have expected EA would work like that. Guess I'll test it myself just to be absolutely sure. In fact i wanted to copy your part, but when I saw the "+50% percent spell power" for siphon life my first impression was it couldn't be right :-) I'll have a deeper look into the matter now.
Hopefully, I'm almost at the point where the damage estimation is good enough to start with the next part (The equip), but I want to fix this stuff first as the equip is based on it.
Many of the answers you're looking for, all in here: