Pretty sure that out west (wide open country) high volume is a real plus. You guys have a real plus in that you can see way out there and observe the reaction to your calls. I believe higher volume in the heavy brush country I hunt is an advantage because the brush muffles the sound; can I prove it, NO. Can get a snapshot of their reaction when they break cover occasionally and come down a sendero or pipeline, but as often as not, they just pop out of the brush right at the call and you have no idea how far they came to get there.
I'm sure that starting right off at high volume has spooked a coyote or two over the years but cannot prove the theory. I do remember vividly one case in particular where I parked the truck, walked forty-50 yards as quietly as I could down the edge of a gravel road to an intersection and set up the call. As usual, I usually sit w/partner watching my 6, and I'm mounting the rifle on sticks (while looking just over top of scope pointed down the sendero) I expect them to come from. Got settled in and fired up the call (usually 3/4 volume. Minutes, if not seconds after the call started, a coyote burst into the sendero between me and the call. He was so close (and so fast) that he was hidden behind my rifle scope until he was in the middle of the sendero! No chance in hell of getting the rifle on him........he blew right past the call and disappeared into the brush as quick as a cat can lick his rear end with his tail up and his tongue out!!! It all happened so quickly, he had to have been very close to get there that quickly.
I know this is just one coyote on one day, but do you think that the volume spooked that coyote? I don't. Has my use of high volume spooked some close coyotes? Probably, but I cannot prove it one way or the other. What works one place may not in another.