Another thought is to possibly set up in the edge of the woods, especially if the field is on the downwind side. That could give you enough break-up that the coyotes don't see you as easily and they should end up circling you downwind anyway, which should present you with a nice clear shot.
I can't say that I've hunted coyotes using this technique, but it sure works well for foxes.
I hope this helps.
Jim