Does Sun Fac's Crit Chance Down need potency to hit?

I have only been running SF for about a week or so and use him a lot now.

I understand tenacity is top priority when modding him. I have some potency on him as well so Crit chance down will hit against the Wiggs teams.

It seems to never get resisted though. Which is weird, unless it just applies automatically regardless of his potency rating.

Anybody know how this works? If potency is totally unnecessary with him I could find non-arena toons to put some more potency on.