I believe you get higher distortion levels the closer you get to the flare frequency, so it tends to be better to keep crossover frequency an octave or more away from the flare frequency... Although I don't think you'd have serious problems?A lot of the times this is simply a cosmetic thing, I believe Wayne has mentioned this as a reason for suggesting a lense like the CH-3. An actual 1600 Hz lense would look kinda goofy on such big speakers.
Adam