My guess is that you just don’t have many fox because you have good numbers of coyotes. Fox are far more tolerant of living and hanging around people than coyotes.
Reds are more wary than Grays by a good margin, but easier to convince than most coyotes. Reds are less likely to show after coyote vocalizations, but not 100% on avoiding. Bird, rabbit and rodent sounds are best.
Grays don’t care about coyote vocalizations in my opinion. I’ve had them show up to vocals and just sit and watch. Gray fox pup distress is deadly for Grays. They cannot resist charging in when they hear it. I think Gray fox would show up if they heard a snicker bar being opened! They are not too smart or cautious.
Gray fox pup distress and gray fox fights are also effective on coyotes for the record. I have NEVER called a thing to red fox vocals. EVER!