spiff,
Since you had mentioned that "The upper-bass cleared up quite a bit" after placing the M60s up higher (you mentioned 16 inches), did you change your listening height as well or did you still sit at the same spot as previous listening before you upped the M60s?
I'm wondering if the bass clarity you heard is due to the fact that the M60s tweeters were now much higher than your ear level taking away some of their direct treble, while the midrange woofer would be directly inline with your ears enhancing this sound range, as opposed to this clearing up effect coming from a removed floor interaction.
I was under the impression that you elevated the M60s a bit, but not a huge distance. Sixteen inches is rather substantial and should change the sound of any speaker moved in a vertical direction by that amount.
