MTM vs TM ... advantages/disadvantages ?

The sound projection axis of a MTM goes straight out, whereas a two-driver system axis tilts up or down depending on whether the tweeter is above or below the woofer. Thus the listener's distance from the speaker has less effect on how it sounds. Besides, it looks good.

Two mids driving the same frequencies will have an interference pattern. The response will be greatest when the ear is at the horizontal level of the tweeter (mid point). The off axis response (ear position above or below the mid point) will have some cancellations at certain frequenices. In practice this makes the "MTM" a poor design over TM for near field applications where your seated or standing position may vary. For applications at a distance this design works well (as in vertical stacked arrays at a sports stadium), the sound beams out from a line array in more of a cylindrical pattern than spherical, and for lagre arrays the sound decays at 3 db per distance doubled rather than 6 db (useful when you want good audibility at a far distance in the rear without making the people at the front suffer from overly loud sound)

Very interesting ! From Shadorne's perspective , the MTM would not be a wise choice in a nearfield situation such as mine .
Very helpful and kept me from making a mistake !

As always , a wealth of information at my fingertips !
Thanks people .