Sounds pretty typical, Pyro. Also sounds like some of the mirage you were dealing with was heat coming off the hot barrel. The shades would help with that, but not with the mirage coming off the ground.
Shooting a Swift or a .22-250, there are probably times when a 20x or a 24x would work, but a 12x will deal with a much wider variety of conditions and is probably all the power you would ever need for a .17 or .222 or.223 class rifle, most of the time. IMHO.
Hopefully Duce or Rifle Dude will chime in. These guys have done a lot of this kind of shooting.