I'm probably way off the mark here, but...
... I don't see how inch power is related to forward pressure in Chi Sau.
The inch power (or less than an inch) that I've seen my Sifu issue, is about creating a very explosive and power hit from next to no distance, whether the attacking hand be a punch, palm etc. (He can also create this with man geng sau, and it would surely result in severe whiplash).
I didn't think I should be using that amount of force (I wouldn't call the power generated in the hit 'pressure') when I was rolling. In fact, I clearly wouldn't use this when rolling, and I think springing forward when a gap appears during Chi Sau has little connection with inch power (other than the fact the two are both moving forward).
But maybe I'm way off the mark and have misunderstood what is being said (it wouldn't be the first time). :)