I honestly have no reason to doubt that fire makes up most of the damage. I presume Torc meant overall base damage when he was describing the amounts. There are a LOT more ways to reduce fire damage than there are evil damage.
going by the 80% and 20%, and using the damage numbers you gave; Lets assume base Fire damage is 4800, and base evil damage is 1200.
Only MRR affects Evil right now (unless you have the raid shield), IDK what your MRR is, but mine is 100, so that would be .5, making that 1200 = 600
Now the fire damage.
53% Artifact Absorb
50% Sheathe
50% MRR
9% from Arcane PLs
gets down to 578.
I also have a HGS item i use sometimes, that gets it down to 354