Sorry, not at all sure at to what you've posted actually relates to?
Anyway, it makes little sense.
Here's a Yamaha response to what?
For a start, you'd not even get the AV receiver to complete the calibration if you connect just one back surround to any of the current models or the models that preceeded them. Secondly, yes, most 7 channel soundtracks do include independent anf not monaural back channels. Atmos in particular uses the phase difference to place objects.
My single back surround channel is calibrated. Would you like a screen shot as proof?