I'm pretty much a veteran fox caller. If you're planning on calling foxes there's really no reason you can't expect nearly all your shots to be inside 75 yards with the most of them being inside 50 yards.
I think the 22 magnum loaded with the faster light weight bullets are as near to perfect as you can get for calling foxes. My personal preference is the CCI TNT 30g HPs. This load will hardly ever exit on a fox at nearly any angle. It'll also drop a fox like a bad habit easily at 75-100 yards with a decent chest shot. I can assure you that if you choose a 22 magnum for foxes, you won't be sorry.
I myself use a Ruger 77 Hornet for my main calling rifle. That's because around here anymore, you're as apt to call in a coyote as a fox, so the Hornet is about my only option for killing foxes, bobcats, and coyotes with consistant results, using the same rifle. With the Hornet though, you have to use a heavier bullet, at a little less than full power to keep from blowing up a good fox hide. I still have to watch my angles though or I'll tear one up pretty bad anyway.