That's the problem with ring radiators on a flat waveguide. It happens to all of them, up to and including the fancy silver-spike ScanSpeak ones.
I recall a while back Emotiva had a traveling roadshow that went to several hotels, including the then-Ritz Carlton in Atlanta (since rebranded "Whitley"). I don't remember the year, but for perspective in audio time, it was when their XMC-1 processor was still well-hyped vaporware, with no working Dirac, etc. I mention that because the speakers they brought for the showcase system were the big flagship Polk towers of the time. The ones with the racetrack bass units that look like Revel Studio2 if you squint a little. They're good speakers and they looked the part, and it was clear from the sound Lonnie and team spent some time EQ'ing the bass in that room to sound pretty good, but the overall sound in the hotel conference room was darkl. Yet if you got up to one of the speakers and put your ear on the tweeter axis it metaphorically bit your ears. The reason is the inherently narrow HF dispersion of this tweeter geometry.
Interestingly, a contoured waveguide seems to widen the HF dispersion of these drivers, both perceptually (which might make sense, given that the whole pattern is narrower) and measurably (which is pretty freakin' cool to me).