What I realized after playing the 7.1.4 test tone is that, despite the fact that the Sonos Era 100 has two tweeters facing opposite directions, it outputs sound from only one same tweeter when playing the side-channel and rear-channel test tones. The other one tweeter is not used... This is why playing the 7.1.4 test tone sounds like playing a 5.1.4. This is a waste of potential. If the side-channel and rear-channel were played from different tweeters, the channel separation would be much clearer. I suggest this.

(The surround speakers of the LG S95TR and Samsung Q990 series soundbars also have separate tweeters for the side channels and rear channels.)