The thing to realize about the canopy is that as you cut slices off the bottom incrementally, to ease the canopy into the proper fit, it changes all of the dimensions as it starts to settle into place. I worked on the front fit first and then the back and as I did, the canopy fit changed depending on how much I shifted the canopy forward or aft. That's what I mean about all of the dimensions changing - and why it is important to "sneak up" on the perfect fit just a little at a time. BTW, I ended up cutting past the trim lines and all fit well in the end. YMMV
The other thing I learned was that it was best if I clamped the canopy to the frame (for each test fit) at my location marks in the front bow first, and then from the aft end forward, because the forward 3/4 of the canopy already fit very close to the natural curve of the frame. So getting the front to lay down was the easy part. At one point when I was very close to the proper fit, I once clamped from the front towards the back and it changed the fit so much it that the aft end of the canopy no longer touched the frame - there was a 2" gap there...and I had a mini freak out! But when I realized what happened, I re-clamped from the aft end forward and all was well.
I was also told by Van's support that the front windscreen fit line was more of a guideline than a rule - as long as you don't conflict with the front baggage door, you are good to go.
I also know of at least one builder who, after making the big cut at the windscreen, cut the forward part of the canopy (think Targa strip), to shift the whole canopy forward...so do what works - just do a little at a time.