When asked for feedback on a 90% completed project you simply shouldn't comment on the big picture, that's set, the feedback is about what small, tactical changes can be done to improve the invested effort. While at 30% things are more strategic... are you missing an essential part? can it be restructured?
I think this post exactly encapsulates the pattern my wife and I have settled on after 15+ years of lively (sometimes embittered?) discussion. Now, we've learned to always ask: "are we editing, or scoping", or "tactical or strategic"? Asking what sort of feedback someone is seeks is essential to non-frustrating communication and having your review received properly -- in a manner that is actionable.