It certainly seems like it should, but I tested it tonight and got no extra damage whatsoever.

I run the same team on UNM every week: Lamasu, Fyna, Lydia, Sulfuryion & Marius.  My best run ever was about a month ago when I hit 192M.  

My Fyna is the cornerstone of a High Elves Siege Team, and she is normally geared in 5 pcs Protection & 4 pcs Bolster. This week, I decided to test her out in 9 pcs of Protection and I expected a noticeable boost to my total damage since her A3 is putting 3 buffs on everyone and her A2 is putting 3 more on a single target.  In my case, Marius, so on many of Marius' big hits, he would be wearing 6 buffs from Fyna, which should equate to a 30% boost to his damage per hit.... 

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 I did 186M last week in Fyna's old gear.  6M shy of my best run. 

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I expected to at least crack 200M and set a new Personal Best with the 9 pcs of Protection on Fyna, but acutally only did 188M, with Marius slightly improved and Sulfuryion & Lydia slightly worse, which should not have been possible? 

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I run UNM Chimera on manual every week, and nothing went haywire with this run.  There was just no improvement whatsoever to the damage per hit, which makes me wonder what the heck is going on?

Anyone have any ideas?