HomePod turns on TV - *not* desired behaviour
Since upgrading to iOS 11.4, every time I ask our HomePod to play music, it also turns on the TV connected to an Apple TV 4K, despite not being told to play there as well. I'm listening to music in another room, and the TV should stay off.
This seems to be an effect of AirPlay 2, but I don't want my TV to turn on any time I ask the HomePod to play music, unless I specifically tell it to play music "everywhere" or on the TV. There must be a setting somewhere to instruct the HomePod to play any requests for Music only on itself, but darned if I can find a way to set that!
(I'm finding the whole iOS11 HomeKit interface just a little too obtuse. By "hiding" complexity, it's become a rabbit's warren of modal secret pathways to getting anything set up. Anyhow, this question isn't specifically to complain about the HomeKit app.)
Can anyone point me in the right direction?
HomePod, iOS 11.4, AppleTV 4K