Messages custom ringtone?

[mdobin]

I posted this in the general help form and received a response from a pixel user whose strings screen is different. So I thought I'd try here.

I've always been able to set the default notification sound for the messages app. It was either in system settings or the app itself. With the RCS chat app update, it seems that I can only set the notification sound by conversation, not by default.

Has anyone found where this setting is buried?