Excellent post! This is what I do with my variable scopes. I verify (at the range) the scope's zero at the magnification I'm going to be using for that kind of hunting and then I leave it there. If I DO need more magnification, I'll crank it in but I'm always aware that scopes (even expensive ones) can and do shift impact upon power change ESPECIALLY as they get older!
One thing I used to use and it really did work was a bore sight. I had one of the old Bushnell models. I would zero my rifle and take note of where the bore sight's setting was. I then wrote that down in a notebook. If (for any reason) that scope didn't produce that bore-sight setting, I knew I needed to make an adjustment which was ridiculously easy with the needed setting right in front of me. It worked well and quite frankly, I need to get back to using that method. Only takes a few seconds to check.
