My Trimble uses a system where all passes are parallel. The degree heading will change ever so slightly as you work N-S passes and get farther away from the original A-B but the passes all stay parallel. At my latitude, we change the heading by about .005° on a quarter mile wide strip. Depending on how far north you are, you'll see a bit more variance.

I believe the JD system uses the exact same headings for each pass and will give you passes that are narrower at the north end -- in this hemisphere. Things will be different in Oz.