I don't know that it helps, but when you don't see a coyote come in to your call it doesn't mean they weren't there. You might be inclined to give up on an area because you aren't seeing coyotes coming in, but take heart. On my very first trip out for coyotes, we'd heard them in the distance, and I never saw one come in, but as we went back to our rig, we saw fresh tracks where they had come in down wind of us. When they got our wind, they boogied. That is going to happen.
If you are seeing scat in an area, you aren't totally wasting your time (in my view).
It also takes time to develop an eye for seing the critters. I recently glassed a hillside before leaving a stand, and saw a coyote walking away from me at 500 yds. How much closer was he earlier? I don't know, but I sure didn't see him. It takes seeing a few before you will see "more".
I must confess to have sat on a lot of 'dry stands'. Be patient. As Jerry signature line sez "its the hunt not the kill". Enjoy the battle.