Question about skill 'more' multiplier

[Ghilgamesch]

Poe's got those certain skills that feature a high degree of 'more' scaling built into the skill itself like scourge, divine ire, incinerate, etc so my question is does that stack additively or multiplicatively with sources of 'more' from support gems?

Example:
Divine Ire 110% more damage with hits x 19 stages
so supports like controlled destruction or elemental focus would be happy dogcrap as the skills more multiplier is already in the thousands if it's all additive.

I'm guessing it's all additive but just want to know for sure.

[JazzyJ]

All sources of "more" damage are multiplicative. Level 20 Controlled Destruction will multiply your damage by 1.39.

[Ratt]

"x% more/less" always means multiplicative and "x% increased/reduced" always means additive (with other increased/reduced, then multiplied into flat values from base, "x added", and "x to y added"), but each "x% more y per z" is additive with itself and then multiplicative with everything else.

For example, you inherently have 4% more damage per frenzy charge, but having the default cap of 3 of them is 12% more damage (damage * 1.12), not three instances of 4% more damage (damage * [1.04^3] ~= damage * 1.125).

In this case, Divine Ire says "beam deals 110% more damage with hits per stage after the first", and it can have 20 stages, which is 19 after the first. This is a "more per" modifier, so it first determines the value of x per z, i.e. x*z (110% * 19 = 2090%), then grants that as a single "more" modifier to y (2090% more damage, i.e. damage * 21.9).