Like the Cardas Caps they don’t having to be shorting type caps to be effective.These are good for nothing sound or noise wise.
Like Al said,
"a shorting plug will have electrical effects, by lowering the input impedance of the unused input to essentially zero ohms. Low impedance circuit points are inherently less susceptible to pickup of electrical noise than high impedance circuit points" " caps that do not short the input will do nothing other than perhaps reducing oxidation or corrosion of the ground shell that may occur over time, and keeping out a few dust particles."
Cheers George