Yes, symmetry is important. You might try toe-in that focusses the on-axis just behind the listening position, rather than in front. But, this won't fix your center image problem. Try setting the balance at the preampa mere quarter or half dB could do it. I suggest using pink noise and an SPL meter to get left & right speakers in balancefar more accurate than by ear. I have one system in an asymmetrical room. It requires the left channel to be .5dB lower to balance.
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