Valence will consider what is in your library, what you play, and what your favorites are. That is basically how it gets a sense of what you like, overall.
When you seed Roon Radio with a song, or Genre, that is the major criterion for what Roon Radio will pick. And when doing this it considers other Roon user’s experience to come up with suggestions via Roon Radio. So how you compartmentalize your favorites likely does nothing. Roon Radio doesn’t use a whole playlist, as a composite, for selections AFAIK. Albums, single Tracks, Artists, Genres are the seeds.
Also be aware that Valence is more than Roon Radio. That same engine will make new music suggestions and will assemble New Releases for You, among other things. Those considerations are based more on your music characteristics more broadly.