Potential issue with enemy damage calculation for projectile attacks

This might become moot post patch, but it seemed excessive enough to at least indicate as a potential issue.

In the Savannah map there are Sandflesh Mage enemies, which seem to ignore part of the damage calculation, or are otherwise incredibly out of tune.

My defenses are as follow (this is on 0.1.1g):

17k armour (During testing, actual value was 17-24k depending on combat buffs)
84% fire res
83% cold res
85% lightning res
79% chaos res

Projectile Bulwark passive causes "Defend with 120% of Armour against Projectile Attacks."

Other regular (non-magic etc) mobs do 50-100 damage per hit, while Sandflesh Mages deal about 300-500 damage per hit. Before getting the Projectile Bulwark passive, it was more like 700-1000 per hit.

Map modifiers were:
Level 79
x% increased magic monsters
x% increased number of rare monsters
Monsters are evasive
Monsters have x% increased ailment threshold
Monsters have x% increased stun threshold
x% increased pack size
x% increased quantity of items found in this area
x% increased waystones found in area

I've noticed a similar issue with projectile fired by a lizard-like mob, I forget the map and specific mob name though. I assumed that was due to it dealing poison/chaos damage, but now I think it might be something with the damage calculation for enemy projectile attacks?

Anyway, it's just a hunch.