Quote Originally Posted by paul_pci
I think positioning is often the key. I recently did some rearranging to bring my center closer in height to my main bookshelves and there was great improvement. The more in line, height and evenly spaced apart, the better the imaging.
Well said.
I set up an insane amount of HT's for people for a guy who doesn't work in this industry. One thing I've learned, is that an inch or two in any direction can really throw things off.
Not just in SPL or delay terms, but the angle and tonality of the speakers.

Matching levels and delays is critical too. I've seen a lot of setups where speakers weren't level matched, It's usually something like the center was 5 dB louder than the mains, the rears were 8 dB louder because there was no sound coming out of them. So when surround imaging is employed, it's all collapses towards the louder speakers, and does't create the desired image at all. Focusing audio is much like focusing a set of binoculars. Proper set up is key to getting the most performance out of your system.