Have you measured and set the sound level of the center channel using an SPL meter?

I have found over several generations of B&W speakers that the center channels often have less efficient ratings and therefore need to have the level trimmed higher to match the front left/right. My current setup needs +5db in the center to match SPL across the front speakers. In my case I also angle the center channel up slightly towards the listener since the console it is placed on is substantially lower than ear height. I use two of the angled foam inserts from a pair of auralex mopads which helps decouple the center from the console and get more on-axis response at the listening position.

All of XenonMan's suggestions still apply, moving the speaker even just a few inches or changing the listening position could have an impact.
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Outlaw Audio Model 976 / 7700 / Ultra-X13
B&W CM9, CM Center, DS3 (side), DM303 (back)
Blue Jeans Cables (XLRs, Canare 4S11 Bi-wire, HDMI)
Tivo Bolt, Xbox One X, AppleTV, LG C765P
Roon, Allo Digione, Sonore MicroRendu, Uptone Audio LPS-1, Peachtree Audio Nova 150
GIK Acoustics Soffit Bass Traps, 244 Panels, Monster Bass Traps, QRD7 / Polyfusor Diffusers