I'm playing on a private Interlude server with some custom weapons.
Anyway, we've got this weapon Icarus Disperser Critical Damage which Increases P. Atk. by 559 during a critical attack.
An Angel Slayer Critical Damage Increases P. Atk. by 265 during a critical attack.
Now i've been testing a bit and i get these results:

Backstab with +3 Angel Slayer no SA = Around 1080 dmg average.
Backstab with +3 AS CD = Around 1260 dmg average.
Backstab with +3 Icarus Disperser CD = 1300 dmg average

So the CD on the AS increases my dmg from 1080 to 1260 = 180 more dmg, thus CD SA that increases P.Atk with 265 on crit gives 180 more dmg.
Now logic tells me that CD SA that increases P.Atk with 559 on crit should increase my dmg with 559 x (180/265) = 379 resulting in an average of 1080 + 379 = 1459 dmg

Could anyone confirm my calculation?

defense?p def still resists dmg..the score will differ all the time imo..

Try the same test with vicious stance on and off and i will tell you if it's correct or not. The algorythms are the same.

From what i see there, that's pretty correct.

Ofcourse by testing i mean i did all blows under exactly the same circumstances, 20 blows each weapon, from exactly the same angle, thus pdef isn't a factor.
I'll look into the damage on VS.

this equation dont have to be linear. it is only a quess.

true, but it's not really logical to have a non lineair equation for this damage.
I mean, why whould they do that? it's a bit easier and more synoptic to just get a lineair equation and adapt the CD bonus to the increase in damage desired.

the problem is that u added 379 to the 1080 from the ANGEL SLAYER, instead of adding them to the damage of the icarus itself

Well it has more P.Atk then the angel slayer, and i've heard blow dmg is not affected by this, I dunno :/

anyway here are the tests with VS:

Backstab + VS

AS +3 = 1785
AS CD +3 = 1966.4
Icarus Disperser CD +3 = 1942.6

The disperser thing must be a pure coincidence. But i think you changed your target. Do this: WITH vs on and WITOUT vs on. Anyway, the cd is pretty accurate, it's supposed to give 200+ dmg on an as. It's not exactly correct, but it's close.

imo SA on that disperser is facked up :]

I think the same. Its crt damage gives almost as twice as patk as the as, so the results should be the same too.

I didn't do the tests myself, another guy on the server i play on did them.
I asked him if he had the exact same target under the same circumstances when he did it with VS on, and he assured me he did, and that his VS was +0.
I never had such an incredible increase like this with my VS +5, so I geuss he just did something wrong while testing.
Anyway thanks for confirming the bug, i'll let the dev know it should be changed .