if you disconnect one of the pair of centers,
does the anomaly lessen, or disappear completely.
try it first with the lower disconnected, then the upper.

this may help you decide if it is an issue of room characteristics , or a issue of phase cancellation.

i just got a regular vp100, maybe one day a vp150.

hth
randy

Axiom M80, Ep600, Qs8, VP150, Crown XLI 2500 , DBX Driverack PA2, Focusrite Scarlet 2i4