What %magic damage is spirit giving you?
EDIT: This is my logic…
(listed sheet 2 damage value for vit) / (total %vit damage + %total magic damage) = base vitality damage of RE
Do this calculation with PoT3 on, and again with it off.
Compare the difference in base damage values.
The %difference should hint at how the conversion mechanic is working here.
What % difference is that – like, ~2%?
I got it. For some reason, PoT3’s conversion is occuring at the same level as your belt.
58 marbles + 46 marbles = 104 god damn marbles
58/104 = 55.7%
Which amounts to ~2% conversion lost.
But this would mean that leaving PoT at 11/12 or sth. would be enough to remove the danger of harmful conversion, right?
Because I start losing vit dmg at 4/12 PoT, already (only 24% conversion)… 
Does it? You should try.
EDIT: Just read the 4/12 POT thing.
Um…can you repeat the same calculations for the fire damage? Like before PoT3, what’s the base damage value.
After PoT3, what is the base damage value.
Then we can ascertain how much of it is actually being converted, because your fire damage DOES dip
It looks like the PoT may come between elemental and global. Assuming elemental is indeed first:
elemental 50%
Pot ~45% fire->acid
offhand ~45%fire->vit
So your image shows
9343 - 8993 = 350 difference.
elemental 129 fire x .5 ~65
Pot removes 45?% * 0.55 ~ 36
36 x 0.45 ~16 remaining converted
without PoT you should see 65 x 0.45 = 29 remaining converted
29-16=13 x 21.5 ~280 (2150%vit)
I’m just using numbers from GT averages but this is in the ballpark. If this result matches really close with your precise item rolls used in the calc…then this might be the case.
I think you might be correct, hammyhamster!
But why does PoT3 even do that? 
Is it because CDR is just too powerful and Crate wants to prevent us from taking it on every build it even remotely fits into?
muhfucken hammyhamster with the numbers. #iloveit
EDIT: But that should also mess around with cinder’s damage value even with 1/12 PoT3, no? So why does this really only impact RE at 4/12 or higher?
Hmm, dunno. You just blew up my idea. Maybe the increased vit% offsets the conversion loss at the lower conversion values?
^Might be a good/different way of approaching the problem.
4/12 is just the lowest I could get PoT3 without unequipping gear 
sorry for the confusion
Then it seems hammyhamster is right. Does the DPS loss start to increase the more points you put into PoT3?
Here’s a weird fact, though:
I just noticed that with both PoT3 and Darkflame Chestguard, my RE fire dmg actually disappears completely…
Shouldn’t there still be 5-7 points of it left after hammy’s calculations?
I despise you. 
EDIT: (actually reply to follow)
Follow you where? Into some dark alley to get brutally murdered?
if it’s not 100%, indeed so. Ahh…I’m probably incorrect, then. 
Maybe it’s worth reporting as a bug if you 2 can’t sort it out.
Hammy, how are you getting the 36 again?
36 assumes that elemental converted 1/2 and 45% of remainder was removed by PoT. (guessing ~15 points in PoT)
Shouldn’t it be 29?
129 * 0.5 = ~65
65 * .45 = 29
PoT removes 45% and that leaves 55% remainder fire. But it might just be a numbers bug in the PoT thing. You can always report it.
Crate is pretty good about saying if it is bug or working as intended.