Soul Mantle curses with 80% MORE curse effect completely negated by 100% reduced effectivenes?

Pretty much the title.

As far as I have understood a curse starts with 100% effectiveness and Soul Mantle curses you with a curse that has 80% increased effect for the total of 180% effectiveness?

If I then reduce that effect by 100% shouldn't I still have 100% * (1 + 0,8 - 1) = 80% curse effectiveness left to mitigate? Or have I understood the general concept of "increased and reduced" calculations?

I noticed this when I was no longer affected by the curses on me after reaching 100% reduced effectiveness while having increased effect on the curses on me.

Is this intended or have I lived in a lie for my entire POE journey? :D

This is because of increased/reduced & more/less being a seperate modifier.

First increased/reduced always is applied additively (multiple sources add up/subtract)

so 100% effectiveness standard
- 100% (from 100% reduced effect)

= 0% curse effect

then more/less apply where each source is applied multiplicatively

0% x 1.8 (80% more) = 0%

Hope this clarifies it.

Yeah, I realized that one just after posting and I guess the math checks out, but I wonder if this is intended? Feels kinda broken to me :D

Edit: But for example with mana multipliers the MORE/LESS part is added before increased/reduced though.