If comb filter distortion starts at 9,000 you'll hear it as loss of sparkle. Problem is that the line array's sound stage and lack of distortion may mask the lack of highs unless you can hear another line array with much higher start up of comb filter distortion as a comparison.

Before I hooked up the tweeters, I ran the system with the 3.5 inch middies running full range. It sounded great, but the comb filter distortion from a 5 inch center to center caused a huge loss of upper frequencies. I didn't realize how much better is could sound until I connected the tweeters, and comb filter distortion didn't start until pretty near the limits of my 58+ year hearing(15,800 hz).

Marlboro