I use an M3 for my center channel and in many respects I found that it actually has a little better wide angle dispersion than the VP150 and the voices sound a little more natural. That is why my VP150 is sitting in a box in my basement.

For that reason, I would recommend that depending on the positioning of it related to your monitor and L/R speakers, you leave it upright and tilt it(if necessary) toward the listening position.