rear firing tweeters....

I had those Snells. E-IV, I believe? I liked them, but not necessarily because of the ambience tweeters. I think they were just good, high-value speakers.

To me, it seems a rear-firing tweeter is basically a reverb unit. There will be some delayed arrival at the ears, delayed enough to not cause phasing errors, but perceived more as an "echo". Ultimately, I'm not really comfortable with intentionally smearing the HF response in time to add "ambiance" beyond what is captured on the recording (or not).

The goal, at least for the Revels, is to smooth the polar response.

Sonus Faber seems to like the idea.

The explanation I heard was to balance out the speaker's power response such that the tonal balance of the room reflected sound better matched the direct sound at the listening position. A rear firing tweeter is not the only way to achieve this goal.

I meant VR-2 my mistake and apology. It does have a volume potentiometer as mentioned above, but it's functional range is very limited and on the low side.