This is what I was talking about. If you look at the two "trucks" you will see the one that is chopped has a shorter distance between the vertical line up from the bottom of the windshield and the top of the windshield. This shorter distance gives the illusion of the windshield not having as much of a rake as it did when it wasn't chopped.
So when I chop the top on my new cab (I started it a few years ago and went onto other projects) I will be lengthening the roof half as much as needed, then rake the post back the remainder so that the roof has a better more "stock" appearing flow.
Get it? Or do I need to get a bat and beat it into you?