I've been trying to find out the % damage increase FW provides, but testing it on a dummy is a pain, to say the least. Best i could come up with is ~23% on top of every special/auto-attack, while FW is up, but the low no. of iterations means there is a rather substantial error margin.
Apparently there is no up to date portal/guide that explains armor mitigation mechanic, or if it is, I haven't found it. I presume that the physical damage mitigation doesn't scale exactly linear with armor rating, there has to be some form of DR tied to it. Perhaps a better question is does FW reduce the direct physical mitigation from armour, or just the armor rating?
Is there anyone with the theorycrafting skills to lend a hand with this? I suspect Simcraft would provide the answer rather quickly, but I lack the know-how to set up a simulation, and doing dummy trials is an option I would rather avoid