Mod errors

[(XBOX)UnbornDa3mon]

Hi, I was wondering how these mod percentages work mainly because of something I noticed when using two mods in particular, vicious spread and tainted shell. I'll explain, my tainted shell is -63% spread and my vicious spread is +60% spread, now I will say I'm not great at the whole percentages thing but to me tha should more or less cancel each other out basic maths right? However it doesn't, in fact it weighs very heavily on the + side, like this, my base accuracy on Arca plasmor is 9.1 add vicious spread and it drops to 2.1, and if I put tainted shell on without Vicious installed it's 24.6 now if I put them on together it's 2.5 which suggests it's not adding -63% of the base 9.1 or even the 2.1 its actually closer to 20% of the newer 2.1 figure but which ever way you look at it the math is wayyyyyyy off. Like I said I may be missing something so feel free to explain what and where.

[(XBOX)R3d P01nt]

https://warframe.fandom.com/wiki/Accuracy#Spread

Not saying you're wrong or anything, but it's very difficult to know if this is a bug or not due to the accuracy equation being unknown to us.

[(XBOX)UnbornDa3mon]

And that's why im reporting it because I don't know if it's a bug or not. I hope its a ui glitch of some sort. One quick point though, I did try the same thing with one other mod to see what would happen, vigilante arms +45% fire rate against Tainted shells -45% fire and they completely cancelled each other out.