Your logic only works if you shoot every fox at 2 feet in front of your muzzle. The .17 remington with a 25 gr. Berger varmint/match bullet will kill foxes at 25 yards or 300 yards with equal efficiency.
Certainly the velocity will be less at 300 yards than at 25, but the fox can't tell the difference.
I sight my guns dead on at 50 yards and they are again dead on at 200 yards. About 6 or 7 inches down at 300 yards. Shot some groups yesterday in about a 10 mile an hour cross wind. The bullets impacted in a little 7/8" group about 1 and a half inches to the right of the bull.
Should work for you as well but then again just my humble opinion. However (comma) I feel that most of the .17 lovers on this board would agree with most of what I said.
Dave
-------------------- Friends don't let Friends shoot Rugers