You've already been given some sound advice, but ill repeat that your RF needs to be on some type of solid/stabel rest to range small objects at those distance with repeatable accuracy. I had the same problems with my Bushnell Fusion 1600's where I hunt (on a power line and a pipeline) I did a couple of things to fix my problem.
1.) Sold the Fusions
2.) Bought a Vectronix Terrapin (best gadget I've ever bought)
3.) Bought a small collapsable lightweight tripod
Problem solved. I can range deer now out to 1,100 yds with repeated accuracy 3-4 times in a row. I'm sure I could go farther, but that is as far as I can see on the pipeline. The tripod will collapse down low enough that i can have it eye level when im laying down prone on the rifle ready to shoot. Ranging is quick, easy, and accurate. Here is a pic of the setup.