I think that part of the problem with poor hits on coyotes ,is due to the nature of calling /baiting coyotes.
Like with deer/elk bear,,whatever...you are waiting,and have time for that broadside/quartering away shot...not soo when calling coyotes.
Coyotes come at ya dead on,,giving you a poor shot,,even when circling to get down wind,,,and you can get em to stop....they dont stick around for long,,some of the best shots you get,is when they stop quartering away...for one last look.
or it could be.....
Same problem i have with SOME deer hunters in my neck of the woods also,,,shootin at tails or hair....i have finished off plenty of em,,holes in rump,through bladder,ears,jaws shot off,,gut shot,leg shot off.....every last one of the shooters,would swear "them deer were tough"......X