Set HomePod as default audio / Stream Directly to HomePod?
Is there a way to make a HomePod the "default" audio setting for an iPad 2 mini on the current iOS (12.0)?
Specifically, I'm using the current iHeart Radio app to stream radio, and I turn off the HomePod either by the HomePod's "power' touch switch or by stopping (not exiting) the app on the iPad. Every time I want to resume streaming, the audio defaults back to the iPad's internal speaker, and I have to manually reselect the HomePod as the audio output.
Alternatively, I've also used a Sonos One smart speaker, and I was able to stream iHeart directly to it with no iOS or other "source" device involved. I believe this was accomplished via settings in the "Sonos" iOS app and which functionality obviously supported by Sonos and probably iHeart as well. I've quickly checked Apple Support but haven't seen any indication that the HomePad can "stream directly" (or that Apple & iHeart allow this), but I easily could have missed related documentation.
Any suggestions would be most appreciated.
HomePod, iOS 12