I don't think this thread is meant to suggest that wider is
automatically better.
I would assume that "wider = lower Crr" is true when you compare tires with otherwise
identical design & materials.
If you switch tire design, then it's apples & oranges. Maybe that's what happened with the Prius people.
EG. I've shown that
my 155/80/13 tires roll significantly farther than my 175/70/13 tires. But (A) they're different brands, and (B) very different tread designs. (I can't speak about (C) the materials in them).