Fists of Fate - how does it work?

I have a perfectly rolled Fists of Fate. “Your attacks randomly deal 1% to 300% of their normal damage”.

Without ANY glove equipped, I crit for about 2.2 million. So in my mind, with the glove equipped, I should occasionally crit for 5-6+ million. 3x damage. But that doesn’t appear to be the case. I never see crits for 5-6 million with the fists equipped.

So I guess I’m confused how this item is supposed to work. Is the damage additive? Does it just apply to base damage and not the critical?

Might be like a lot of items right now that are not working properly.