As long as you are talking about a rectangular baffle (not square or circular) I don't think it makes that big of a difference. The location of the driver, offset or centered, will impact the ripple above the hump in the baffle's response. Compared to other anomolies such as the room, the crossover, and the driver's natural non-flat peaks and dips I think these ripples are in the mud. If you do bias your drivers towards one edge of your OB, and build a mirror image set, you can always swap left for right and try it both ways. Use the positons that sound best. Don't worry the small stuff, worry the big hitters in your OB design like relative driver efficiencies and woofer Qts.