Poison damage confusion

I have a stripped character
The only damage increase I have is from DEX which is exactly 500 for a 50% increase
I have no damage increases from gear or paragon or passives

My weapon damage is 4086
Rank1 penetrating shot says it does 70% of my weapon damage
Rank1 poison imbuement says it applies 100% of the base damage
I am level 100 hitting a level 100 target dummy so there is 74% monster DR
So an imbued pen shot is expected to do:
Weapon Damage * Pen Shot Damage * Poison Imbuement * DEX Multi * Monster DR
4086 * 0.7 * 1.0 * 1.5 * 0.26 = 1115 damage
When trying this on the dummy I am getting 10 ticks of ~110 so this is working as intended

What confuses me is when I use an Andariel’s’ Visage
The tooltip damage shows 24515 which is 600% of my weapon damage
The expected damage is:
tooltip damage * DEX Multi * Monster DR
24515 * 1.5 * 0.26 = 9,560

However it does 10 ticks of 3826 which is 38260 damage
Which is almost equal to the tooltip * DEX multiplier which is 36772
It is as if this damage bypasses the 74% monster DR?

The new patch changed something, the patch notes say 50% buff
Tooltip now shows 36773
The new expected damage would be 36773 * 1.5 * 0.26 = 14311
But it does a total of 38260 so the same exact amount as from before the patch
Also the nova visually appears around the target, but the damage still occurs around the player