Hi jhunt17,
As pmbuko noted and kcarlile stated so gracefully, that "pink noise is not especially representative of how well your center and front speakers will blend with actual movie soundtracks or music," it must be emphasized that pink noise is a brutally revealing test signal.
Pink noise is so revealing of any slight deviations in frequency response, whether caused by your room, interference effects, nearby boundaries, or problems intrinsic to the speaker, that two or three identical speakers in the same room will never have identical timbral signatures with pink noise. That's because a pink-noise signal contains equal energy per octave across the audible spectrum. But when we listen to musical works or movie soundtracks, that never occurs. Content in each octave varies all the time. You can confirm that if you look at any real-time graphic display of music or soundtrack playback. So in effect real music and soundtracks are a much less critical "test" signal. We're far more accepting of slight tonal discrepancies in that we rarely notice them.
But the goal is to locate your center and mains so they have a reasonably close tonal match. Then when you play music or movies, the tonal balance is close enough so you get a nice seamless blend.
And yes, you discovered with your scientific laundry basket test, that a center will often sound its best in free space, on a stand away from the face of the TV display. If you can manage a setup like that, excellent. Otherwise, you have to play around with the center location until you get a reasonably good blend with music or movies.
Regards,
