It doesn't really matter because only the nulls are at oblique angles and only very slightly. That said, They are intended to be built and used in mirror images. This is mostly for aesthetics but there is a very small tilt in the position of the forward lobe and the upper and lower nulls. For that reason, I generally suggest the tweeters be outboard. That way the upper null is slightly to the outside and the lower null is slightly to the inside. But again, it's so slight, it really doesn't matter.