10-25-12: Timrhuyou know, I almost wrote a post yesterday (10/25/12) with the same advice!! ;-)
Turn the speakers upside down.
I looked at it a bit more & decided that it would not make sense because the tweeter is in the middle (with the midrange above & the woofer below). it would have made sense had the tweeter been the top-most. Then turning the speaker upside down would have made the speaker time-aligned & would have accounted for the various acoustical centers.
My advice was going to be to lower the speaker such that the midrange was at ear-level.
In a speaker system that has minimal phase distortion & where the drivers are placed tweeter-mid-woofer going from top-down, then the vocals should come from just below the midrange. In such a speaker this would end up being about mid-speaker.