i am trying to decide if 4 points is worth upgrading this special trait of Enhanced Weapon Throw III : Increases Effect Potency to 40% ?

does that turn the chance to inflict Heavy from 20% to 40%?

or does it give a 40% Potency bonus to the 50 Potency damage is deals?

which if its the case i can't really value a minor damage boost increase, but i would love a higher chance for a heavy to trigger