In times of heavy mirage, I set my spotting scope so it's focused a bit short of the target so that I can easily see the mirage as it moves back and forth with the wind. At times I can actually watch the target "appear" to move to one side or another and snap back. It has helped me to realize that when I look at the target through my rifle scope, I'm not actually seeing the target, what I am seeing is an image of the target projected through lenses into my eye. This image can be easily distorted by different temperatures and densities of the air moving between my scope and the target, my job is to figure out where the target actually is, and how I can hit the middle of it, and it ain’t easy! 

Bob