Reflection makes even less sense than diffraction.
Think of the speakers as sources of light rather than sources of sound. What happens when the radiated light from each, hits a hard surface such as a coffee table?. It'll mix, reflect, even diffract (creating further reflections). Irregular objects on the table will cause break up, but at what expense?. And any that hits the surface will reflect without break up.
Translate this into a sonic sense and you have artifacts that will interfere with the very necessary processes that determine soundstage/image quality: controlled reverberation, precedence, Haas, etc.
If said table is a necessary domestic fixture then i'd mitigate it's detriment with something like a dense foam pad and/or heavy cloth cover.