Mitigation appears incorrect on Dimension Breath (VDH tank)

In Nexus King (Heroic), it appears that some mitigation is not being applied correctly to Dimension Breath. My best hypothesis is that fiery brand is not included.

The logs from our recent fight say that Novidius (me) for one tick of the breath took 1,073,683 of the original 1,761,532 damage, mitigating only 687,849 (39.05% mitigated). However, Fiery Brand was up, which should (by itself) mitigate 40% of the damage. I would expect the following mitigation to apply:

o Demonic Wards: 8%
o Versatility: 12.75%
- Actually a bit higher than this—this is from Wow armory + Mark of the Wild, but doesn’t account for flask.
o Fiery Brand: 40%
o Fel-Flame Fortification: 10%
o Calcified Spikes: 1%
o Devotion Aura: 3%
o Frailty (2 stacks): 6%
o Set Fire to the Pain: 5%
I might be missing some things, but this should work out to something like:
0.92 * 0.8725 * 0.6 * 0.9 * 0.99 * 0.97 * 0.94 * 0.95 = 0.39 = 37.2% damage taken/62.8% mitigation.

If I take out fiery brand, then the math works out to what was observed—approximately 39% mitigation. To me this suggests that fiery brand is not being applied correctly. I would guess that this is happening because Dimension Breath is getting categorized as environmental damage rather than from the Voidwing—since there are also portals that open and shoot out the same beams. However, the frontal from the dragon (that the tank needs to take) seems like it should count as from the Voidwing (which is also how it appears in the log) and FB should apply.

Ignoring the part where the logs say you mitigated ~52% of each tick of dimension breath, base damage of the breath is a lot higher than 1.7mil.

After some careful experimentation, it appears that fiery brand reduces the unmitigated damage rather than showing up as mitigation. Frailty appears to be counted in the same way. This makes some sense given that they are debuffs on the target/how they are phrased, but that was not immediately obvious from the logs.

So there appears to not be a problem after all. Sorry for the erroneous post.