Most people use either a tape measure for distance and then adjust the center channel up or down as they need, or auto-setup/calibration from their receiver/processor such as Audyssey to get things tuned in pretty close.
Whether I am using my current VP180 or when I was using my VP150, I let Audyssey do a full calibration, and then just bump up the center channel a few dB manually. This is for 2 reasons. 1) The most important audio in a movie comes through the center channel, 2) I never want dialog to be overpowered by the effects field created by the front left/right and the surrounds. (gives movies more "punch" to have the center a little louder, and my wife has minor hearing loss, so it helps her enjoy the movies more as well)
