Calling sequence, and exact distress sounds are not as important as stand selection. If you have crows coming in, you're on the right track. If you sound like something that's being eaten alive, you're on the right track. i call a lot at a stand, others call a lot less. I'm seldom on a stand more than 15 minutes., because I can see literally for miles in any direction around here. If it's coming I can see it inside 15 min. In Michigan, I doubt that is the case, so a little longer on stand is needed. you're on the right track with 30 min.
Find an area with coyotes. Sounds simple, but if there is no scat or tracks, there likely aren't any coyotes. Get into your set up as quickly and quietly as possible. Try to pick a stand that allows you to see around you. If you stuff into a clump of bush, chances are you'll call coyotes and never see them. Watch the wind. if you can get a buddy to come along to watch the back door , this helps sometimes.
Keep trying. I guarantee you won't call one from the couch. I live in an area with tons of coyotes. I've got lots of experience. I guide predator hunts. And I haven't been able to buy a coyote the last 10-12 stands. Sometimes they just don't co operate.