Keep in mind that an increase to weakspot damage/headshot damage of x% doesn’t increase the total damage by x%.
Rather, let’s say your attack normally deals 20 damage. But on a headshot it deals 25 damage. So a headshot increases your damage by 5.
If you have a weakspot damage buff of, say, 25%, what that’ll do is take the extra 5 and multiply it by 1.25, turning it into a 6.25
So a 25% weakspot damage buff would make this hypothetical headshot go from 25 to 26.25.