Rules of thumb are general guidelines. Your own trial and error experiments will prove what works and what doesn't. Proportional rules only help at specific frequencies so that no matter what you do, there will always be other frequencies harmed.
An approach I've found more beneficial is to take care of first reflections. Most all speakers need "breathing room"3-5 feet from the front wall, and at least 2-3 feet from the side walls. This space helps sufficiently delay the first reflections. Psychoacoustic mechanisms of the brain can then separate the direct sound from the reflected sound. Delaying these reflections also reduce their volume, often doing more good than random room treatments. It should improve imaging, clarity, and usually give you a more dimensional soundstage.
An approach I've found more beneficial is to take care of first reflections. Most all speakers need "breathing room"3-5 feet from the front wall, and at least 2-3 feet from the side walls. This space helps sufficiently delay the first reflections. Psychoacoustic mechanisms of the brain can then separate the direct sound from the reflected sound. Delaying these reflections also reduce their volume, often doing more good than random room treatments. It should improve imaging, clarity, and usually give you a more dimensional soundstage.