The reason I would rather the woofer and tweeter be one above the other on the baffle is this keeps the path lengths the same as you move from side to side. The layout of the one π, two π and two π tower makes everything just right when you are directly in line with the midwoofer. In this position, you are the same distance from the woofer as you are from the tweeter. You can move from side to side and still be the same distance from woofer as you are from the tweeter. If you reorient the speaker so the woofer and tweeter are side by side, then when you move left of the speaker you're closer to one and when you move right you're closer to the other. This does weird things to the sound because response changes as you move through the room. So reflections from different angles have a different tonal balance too.