[Math] How Exactly Do Corrosive Procs Work?

[Darzk]

I had thought I had a good handle on this. Was doing some testing for another player and came across a couple of anomalies.

 

The build is

It results in 3486 Corrosive damage per shot

 

Problem #1 is this damage against a level 34 Heavy Gunner (1636 Ferrite armor)

If we assume the Corrosive proc comes into play first (making it 1227 armor) and then Corrosive damage which ignores 75% of Ferrite armor, it makes it 306.75 armor, which should reduce the damage of the shot to 49.44%, which is 6032.6 damage. Instead we're seeing only 5980. If we assume the Corrosive proc doesn't effect this shot, only subsequent damage, we should be seeing 409 effective armor, reducing damage to 42.31%, making only 5162 damage for this shot... so obviously the Corrosive proc is having an effect.

 

Backcalculating, we can determine that the damage is being reduced as if the target had 1248 armor (would result in 5981 damage) which is 76.3% of the targets armor, instead of the 75% we expect. You might think 'oh that's such a tiny difference, who cares', but it's resulting in more than 50 damage lost per shot, and I'd really like to know why it's happening.

 

Problem #2 is this damage against a level 33 Elite Lancer (357.3 Alloy armor)

Here we can see that the damage done is being calculated as if the Corrosive proc never took place - 3486 Corrosive damage is reduced by 357.3 Alloy armor to 45.64%, which is 1591 damage. 

 

So why is the Corrosive proc effecting the damage of the shot that causes it against Ferrite armor, but not against Alloy?

[QTEila]

Corrosive is more effective against ferrite since ferrite armored enemies are 75% weaker to corrosive,

 

Alloy Plate however (like bombards) Take massively reduced damage from the corrosiv eprocs but takes massively increased damage from radiation procs (Just like the tenno as we are also alloy plated) 

 

the damage it shows however is just your damage number you hit for, the proc next to it doesn't have anything to do with your damage but indicate you inflicted a corrosive proce, therefore reducing the targets armor by 25% per proc stack.

[Darzk]

the damage it shows however is just your damage number you hit for, the proc next to it doesn't have anything to do with your damage but indicate you inflicted a corrosive proce, therefore reducing the targets armor by 25% per proc stack.

This is true, but in the first ss it's showing that the corrosive proc is increasing the damage of the shot that caused it, and yet in the second ss it's not. And for some reason it's reducing the armor by 23.7% instead of 25%.