I believe we have a WoB that says that enough copperclouds could block soothing. IF that is the case then I have an idea. Soothing works by sending a "ripple" through the CR. This ripple interacts with your cognitive self(like a wave). What I think a coppercloud is doing is producing a bunch of ripples at your location, like static, that masks your location. I imagine spren wood flee such an area(it would be like a highstorm on the cognitive side).