PoE2 "Increased damage with hits against enemies" (eg Hindered Capabilities) and "targets take increased damage" (eg shock,) multiplicative or additive?

I'm having trouble parsing out which "increased damage" effects are additive and which multiplicative. I recently read that increased damage taken by enemies, as in the shock ailment, acts as a multiplier. Is this accurate? Do multiple sources of such add or multiply? The way I'm trying to make sense of it now is that it acts as a multiplicative factor which grows additively if the game takes your post-calculation damage dealt and applies it to the enemy as the base damage to which defenses and debuffs apply, and then this (eg shock) debuff sums sources in the usual way for modifiers with the "% increased damage" language. Is that correct? If not, do you know the correct model for reasoning like this or is the language opaque and one just has to learn the specific rules for each mechanic?

What about Hindered Capabilities, "30% increased Damage with Hits against Hindered enemies"? It reads to me like it applies at the source of the damage (you) and is additive with other "increased damage" effects. Do I have that right, or is it multiplicative? If the latter does it add or multiply with eg. shock?

Thanks for the help!