I have never tried a D'Appolito speaker center channel in that manner. I always have had it vertical and it appears to sound correct in that manner for two reasons; one is speech because it emulates the verticalness of our mouths and second because it gives emphasis to the whole surround sound field. I have tried a two way(tweeter over woofer) set-up and I did not get the above results. My brother uses a Mirage Omnistat 5 channel system with one of the Omni's as a center channel. It appears to work well but I would really need to try one on my system to see if that would work better or worse than a D'App. In owning a few D'Apps, I noticed that some of them have two 4 ohm wooferswired in series and one that I have with two twelve ohm wired in parallel. The latter sounds not only better but correct in its phasing. The trouble is that you do not know what you are getting by looking at the speaker.as a whole till you open it up and test the DC resistance(many think this is not important but I assure you it is very important). Many years back, I made a 5 channel dynaquad system in my bedroom consisting of 5 Minimus 7s of which the center channel was one of them. I did get a rather extroadinary perfomance on dialog from dolby surround tracks but it would only work with the rear surrounds near my ceiling and on their sides to get the effect.

If you feel your soundfield is correct then continue doing what you are doing.