Build question re: item passives, stacking damage calcs [in-depth]

I’m running a Toxic/Scythe Necromancer build that is super fun and has carried me to T16 finally, but as I tweak the items in the kit I’m noticing the damage doesn’t seem to be stacking quite the way I thought it would.

The build is: Cursed Scythe, Skeletal Mage (Contamination), Corpse Explosion (Close Quarters), Command Golem (Flesh Golem), Bone Armor (Dislocation), and Blood Rush (Metabolism).

Kanai Passives: Nayr’s Black Death, Grasps of Essence, and Krysbin’s Sentence.

4 poison abilities = 400% damage boost through Nayr passive.
Max (5) stacks of Corpse Explosion = 1,000% damage boost through Grasps.
Stun on Bone Armor = 300% damage increase through Kyrsbin.

Relevant item Passives to stack with above: Leger’s Disdain, Convention of Elements, and Harrington Waistguard.

Leger’s Disdain grants 840% additional damage to Grim Scythe (so 940% total), Convention boosts each elemental skill by 200%, and Harrington grants 120% increased damage after opening a chest.

Relevant item stats to stack with above (rounding for simplicity):

Poison skill damage + 60%.
Corpse Explosion Damage + 10%.
Skeletal Mage Damage + 10%.
Grim Scythe Damage + 10%.

The combo:

Proxy enemies so they aggro, gather them into a group, then Bone Armor --> Cursed Scythe and Skeletal Mage (4 swipes on average) --> Corpse Explosion; rinse and repeat.

How much extra damage am I actually getting? I’ve been told the “sheet” damage stats (+poison skill 60%, +grim scythe 10%, etc) are applied separately at the very end… is this correct? If someone could even break down how one of these abilities, like Cursed Scythe, gets finally calculated with a full stacking combo, I would appreciate it. I cannot find a straightforward methodology anywhere online, aside from knowing that sheet stat damage is supposedly calculated last. So for example, if I were just to stun an enemy and then Scythe them, would the 940% base damage on Cursed Scythe then be multiplied by Kanai passive damage, i.e. 940% x 300%, or do they just add together to 1240%?

Also I have a pair of ancient Depth Diggers pants which grant additional 100% damage on primary abilities, but it does not have +10% increased Scythe damage stat. I assume anything with a sheet stat is better, because my full stacking passive bonuses will be multiplied by the sheet stat at the end, versus just having 1,040% base Scythe damage instead of 940%. Do I have that right?

Very long detailed post, thanks for reading and sorry to ramble!

Try d3planner and and adjust it to your liking.
https://www.d3planner.com/326110619
The increase in damage from various sources is multiplied.
https://ctrlv.cz/shots/2020/09/04/Valf.png

With Poison Necro, you basically have 2 options in high GR

  • Poison Scythe : Full poison skills minus Simulacrum
  • Corpse Explosion : Full poison skills minus Frozen Lands

D3 planner gives you damage formulas by the way.
Rollover you mouse on damage, everything is explained.