Essentially any AO scope will work. Those with a 25 yard minimum distance may be a bit better than those with a 50 yard minimum. EFR is better yet but not truly necessary. Most fixed parallax rimfire scopes are set around 60-65 yards or so. Anything shorter is an improvement up close, just a question of how much improvement.
The 6.5-20x EFR is a nice scope. Sometimes too heavy for a svelte rimfire. I believe Midway still has some VX II compact 3-9x RF specials with AO, CDS, and their windplex horizontal crosshair. Damned nice little scopes.
Tom
