I've felt the same way before. Stick with it! A couple ideas that came to mind while reading your post are to sit still longer than you think. I don't know how long your typical set is but the majority of the dogs I've called came in between 22-25min. I hear people saying that if they don't come in the first 15 min they aren't coming, but that has not been my experience at all.
Also, I hunt wide open areas too and many times when I thought I could see every bit of ground within 500yds I have had one pop up at less than 100 and had no idea that was even possible, point being that coyotes know how to use minimal cover and blend in well, it's easier than you think to look them over. It took me almost 3 years of calling and failing before I dropped my first coyote, but you learn from the unsuccessful hunts and with some patience and sheer effort you'll get there! It's the challenge that makes it rewarding, cause the meat's not real great
Oh yeah I also though I'd mention that I see way more dogs out the morning after a big storm clears, especially if that storm has lasted several days. So if you ever have a day off when the weather clears, try to get out there!