One thing that you mention that you do, and I read that a lot of guys do it, is to get to your location and sit quietly for several minutes. I see no need to do this. As soon as I sit down and get ready, I start calling.
I call of and on for about 15-20 minutes, longer later in the season when I start using more vocals. Early in the season, I usual very little vocals, and I may blow 1 minute distress, sit 30 seconds, then another 1 minute, wait quietly for a minute or two, then another series over and over. I may even change distress sounds about 10 minutes into the stand. Don't be afraid to try different sounds, even is the sounds aren't something normally found in your area. Coyotes hear distress, they don't hear snowshoe, jackrabbit, and cottontail, or flicker distress. They just hear distress.

Really doesn't sound like you're calling wrong, so it may have to do with your stand selection. As Sheridan said, you've got to set up so that you can see them before they smell you. I dont' worry so much about a coyote seeing me first, after all, I'm sitting still in camo hopefully blending in with my surroundings. Worry more about the coyotes smelling your first, because if they smell you first, then you likely won't get a chance to see them at all.