Em, the clarity may not improve all that much by moving it to the top shelf. What you WOULD likely gain is some continuity in speaker height in that all the tweeters will be closer to being in line with each other. Otherwise, if a car drives from left to right, the sound will"dip lower" when it's in the middle.
Plus, with so much of the sound information coming from the center channel, it will sound more like the voices are coming from the actors if the center is close to the TV screen.
Sorry if I just gave you reasons to take on a project tomorrow.
