I thought this would be fairly easy...but 45 minutes of basic trigonometry, some algebra and a couple chicken bones later, I came up with this:
The math seems to work, and the values are consistent with what I think is going on in reality. I had to actually write it out (gray boxes at the bottom) to convince me I was heading in the right direction. If someone is REALLY interested in the math, I'll post what I came up with.
I'll give this a shot next week, I plan to shoot some close in stuff, so it will be interesting to compare whether I can use this to get closer to the bullseye at 5, 7, and 10. This data indicates I should hold a bit high when I try to nail 1" squares on Find Your Level at 5 yards, for instance.