Pictures will not help much though. Most all setups you'll see vary, even if slightly. I went through this with my CZ 457 (pic up thread). My issue was that I have the CZ American 24-inch barrel which tapers considerably to the muzzle, and I plan on adding a custom barrel later, which will have a much larger diameter at the base of the objective lens bell. I also have a 20 MOA Rail.
The solution? I found this website (below). If you feed careful measurements to the calculators you will get the right answer. I did, so I went with the medium high rings which right now are over clearance for my setup but will be exactly right for a larger diameter barrel. Don't Forget to factor in the lens shade if you ever plan to use one. That will affect the calculations with a canted rail.
Calculators:
http://www.mil-rad.com/
Another caveat. More important than the height of the rings is having an adjustable Comb/Stock. See Frank's article in Gun Digest here:
9 Long-Range Shooting Fundamentals You Must Master