Paul, as I've commented on numerous occasions here during the past seven years, there appears to be no reason for the horizontally configured center speaker other than an aesthetic conviction that it looks better than a small vertical speaker there. Acoustical "design" considerations would argue against them. A vertical orientation of at least the tweeter and mid-range speakers gives wider and smoother horizontal dispersion(even turning an MTM center upright can also show this). Note that some large center speakers which are configured in a W T/M W manner can be interpreted as a small vertical speaker with woofers on each side.
