What caliber do you shoot? 300 yards I would put it on the top of its back and squeeze. Did you try challenge barks? Do you use a coyote decoy? In my experience I believe it's a lot like calling turkeys some will fully commit and come right in and others won't come no matter what you throw at em. A lot of times coyotes will hang up just inside the timber when night calling and bark and howl and make all kinds of noise but will never show themselves. Have you tried calling with a buddy? Put one guy 100 yards in front of the caller in the expected coyote path or if you have a fox pro set the caller 100 yards away at 2 o'clock from your position directly up wind of you but relevant to where you believe the coyote will come from. I believe wind direction compared to the section/terrain you hunt is the most crucial part of trying to call coyotes. If there's a a spot where you can set up that gives the coyote the false impression that they can safely get down wind of the call without being in the wide open by using buffer strips, fence rows, small washouts etc. those are going to be your best producing spots year after year.
