I would guess there are a number of reasons things do and do not work. The coyotes nose, the amouny of scent we leave on things, wind direction, how much we move etc.
What I do know is I killed more coyotes when all I did was walk to a hide, and used my mouth call.
No setting up of anything, other than me sitting down, concealed. Paying attention to wind direction, how much I am moving, and how well i blend in.
And I stopped wasting money on scent masking products. Even if I sprayed myself silly, there was always some area of my body/clothing that let my scent out.
THE ONLY reason I started using electronic calls with a remote, is I hunt alone and several times I attracted a couger, and I was not aware of it.
I was sitting in the middle of a large sage bush I had carved the center out of the day before. I had nothing at my back, to protect me from ambush. Cougers are an ambush predator in the exstreme. Last thing I want to expierience is one of them jumping on me.
I have a friend that is an avid coyote hunter. He lives in a couger populated area. He wears a holloween mask on the back of his head. He feels that sonce lions may not attack you if they think you are looking at them, he is safer than without the mask. I really dont know, but when hunting alone, I can't see the harm in being prepared.