Hmmm... I am not sure how you have come to that conclusion. The polar response you posted shows the HF response dropping like a stone at only 8kHz in as little as 30 degs off-axis. Compared to the Sierra-2 polar response, which at even 90 degs off-axis, is only about 3dB down...
I am not sure if you are properly interpreting the polar response measurements and I am also not sure if you are comparing the Gem's to our Sierra-2 or our ribbon towers.
There is simply no 1 inch dome tweeter made that will have as wide and symmetrical horizontal off-axis response as the ribbons we are using. It's just physics...
I have quite a bit of experience with the Gems (both in listening and measuring as I was lucky enough to work with a few ex-Harman engineers. That said, my comparison was regarding midrange clarity and detail and more specifically with our towers than our Sierra-2. Personally, I was never much a fan of the Gems (any version) as the thinness you mentioned was always a bit off-putting and that same thinness also contributes to the impression of more detail in the mids and highs...
I fully stand by my original statement Both in listening and backed up with measurements. Have you seen the polar response of our ribbon tower? It is remarkable...
srt-polar.jpg