MO Coyotes, the logic side of me is talking here. If a coyote is close enough to hear the "buttons clicking", then they are surely close enough to at least see, if not kill. And I don't see how the rotation of the call could be causing coyotes to not show up. Too loud, probably not, after all there are guys that use full volume, or darn near to it, that post that they are killing coyotes, so that surely isn't the problem. Too softly, well, if they can't hear it, that could certainly be a problem.
I guess I have often thought I found the right "sequence" but what my favorite sequence of sounds is very well probably isn't anyone else's. Heck this year I've killed more coyotes to simple 'ol rabbit then anything else, BUT I have been hunting low pressured coyotes so I expect them to come to rabbit. Once I start hunting my properties for a second time for the season, I won't be using rabbit, probably lean more on vocals.
I highly doubt it's a chosen sound problem, as I think most un-pressured coyotes would come to a multitude of prey sounds, and probably a lot would also come to vocals. Sometimes we fall into a slump and it seems a guy can't buy a coyote for nuthin'. My guess is you're in one of those slumps, OR you're hunting highly pressured coyotes and that is a sure way to knock ones success down, really quick.
Keep after 'em. You'll figure it out.