One exception is the Pro four Pi with the port beside the tweeter. This makes the tweeter slightly offset left or right of the woofer. In turn, the verital nulls are slightly diagonal rather than directly above and below. That means you'll have slightly better vertical pattern control in the direction of the line between woofer centerline and tweeter centerline. So if you have a sloped or gabled ceiling, I'd probably position the speakers where the line drawn between woofer centerline and tweeter centerline was directed at the lowest point.