I think you mean you have the center mounted so that the cones are at the same height as the tweeter/midrange.

It all depends on how you have set up your PLIIx and Neo6 parameters. In DD or DTS, the sound should be focused from the middle (at least that's how it is on mine and it sounds great!).

How far away from the M60s are you sitting?

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated