Barring setup, calibration, and speakers problems, I think Jack hit the nail on the head when he says "no speakers of such different size and shape are going to sound exactly the same". This is why most "experts" recommend three identical speakers across the front. To my ears, I've never heard a "dedicated center speaker" that sounded "right". Aside from the tonal/timbre match problem with small center speakers, is the annoying problem of having the dialog seem to come from below or above (depending on where it is placed) the screen.
If you really want know what a seamless front sound stage sounds like , try the "phantom" center mode just for grins. it's the next best thing to having three identical front speakers (at least for an on axis listening position). You maybe one of a growing number of people who have discovered that they don't like center speakers.
