It has to do with the all horizontal alignment of the drivers on the VP150/180. With all the drivers in the same plane it has a beaming/straight out horizontal pattern, the trade off is this design offers good vertical dispersion for top or bottom mounting of the speaker over/under the screen. The VP160 and its WT/MW design offers better off axis horizontal dispersion like a standard vertical speaker but doesn't offer the vertical dispersion of the horizontal layout, so some may find the sound doesn't come from the center of the screen but below/above where the speaker is located; I notice this from time to time with my VP160, depending on material, I think an M2 above the screen would anchor dialogue to the center.
