Quote Originally Posted by Gemina View Post
No data or link is needed to validate it. It is simply using the formula provided in the descriptions by both abilities.
Eh.. that's not an argument. Tooltips can be wrong, and have been in the past, besides they provide no information about how they combine.
It's a generally accepted theory that it's multiplicative, and I have tested it a bit a few months ago. I can't find a recent source with test data however, so I have no valid proof ready. I might get back to this later, to show some data :P