Generally what these effects look at is your “increased poison damage” on character sheet.
This number is increased poison + generic increased modifiers, it does not include damage over time. Damage over time is a second line.
So for example lets say you had 200% increased generic damage, and 50% increased poison damage, your character sheet would have 200% in every line, and 250% in poison. Thats what it looks at, the 250% in poison. if you also had 100% increased damage over time, your damage over time line would be 300%
if you had something like “poison damage at low life” that would work, or generic damage on low life.
More multipliers that are global and generic show up as well and multiply the value, but those are in short supply.