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Are you doing anything for scent control? My hunting experience for coyotes over the last two years sounds very similar to yours. Scent is kinda the one area I haven't really touched yet, and I am starting to wonder if that will help? I know they have very good sense of smell, I just usually try to plan my stands according to the wind.
I'd also try to incorporate some kind of decoy to your setups. It doesn't have to be anything fancy either. Maybe just a turkey feather tied to a limb or bush, or a small chunk of deer hide on a pull string. I once called in a trio of coyotes from half a mile away, using a stuffed animal on a 50' rope dangling on a small cliff. Killed two of them at about 50 yards.