Omar, there's been considerable discussion of that here. The advantage of the vertical M22 center in having wider and smoother horizontal dispersion is lost when it's placed horizontally and in addition the pattern would be different left/right. Whether these factors would make the VP150 preferable if both were horizontal isn't clear. I've never heard the VP150. My tests five years ago when I got my M22s included horizontal positioning, and it certainly wasn't unacceptable, but neither did it appear to have any benefit over the typical horizontal MTM center.
