I got a chance to take the sprayer for a dry run today in an irregular summer-fallow field. That answered a lot of questions. I see now that I was waiting too long to push the "Headland complete" button. You are also correct in that the A-B could be set on the east edge of the field. No reason to set it on the west. Just set it on a true 180° heading and I should be OK when I get to the fence line.

Hills??? They're kind of like rocks here. Hard to find