A common problem with hunting varmints is the rifle is over scoped, to much magnification. You get something close and the scope becomes a hinderence. I would suggest 1-4x or 1.5x or something.
On stuff, lets say skunk or smaller, parallax issues can cause trouble also, as well as scope height over bore. You really got to be able to anticipate trajectory at closer ranges and small animals. An inch or so can make a difference in a clean kill or shooting the foot off of the critter.