Scent control is not needed, BUT knowing where your scent cone is going is very important. The wide open spaces of eastern CO. allow a guy to set up a stand so that the wind is such that you can kill the coyote before he reaches your scent cone. In other words, kill'em before they get a chance to smell you.
You would probably find calling coyotes in the winter to be more successful for a couple of reasons. Less food available for them to eat and colder weather forces them to eat more and more often. Both lead to coyotes that come to the call more easily.
There's plenty of winter days that aren't cold, and deer hunters are easily avoided on the eastern plains.
The hot summer days are better for sitting under an umbrella shooting priarie rats.