No, and yes. ;)
I think what Sonos is doing so something like Dolby Pro logic used to do, which is create a false representation of what it thinks should be in the surround channel, and sending that. it does the same kind of thing when the surrounds are set up as ambient when playing music, some sort of software best guess. One of the reasons I use full, rather than ambient. Love those software engineers, but prefer the original intent ;)
I'm also set to full but was under the impression this only effects music. Is there any way to stop the artificial surround implementation?
It’s probably due to the backward compatibility of the Dolby codecs that you are listening to a Dolby Pro Logic signal with a technique called ‘matrixing'… see this link as a brief explanation:
https://www.hometheaterforum.com/community/threads/difference-between-stereo-and-dolby-surround-2-0.45530/
To stop the issue, perhaps switch the audio source/TV to 'PCM stereo' and see if that resolves things so that the audio plays through the front two channels only.
Yea, I agree with Ken, I think it isn’t something you can adjust externally without changing the input. And yes, the Full setting only impacts the music, and not the TV input.