As I promised -update:
As up today after reaching 1K miles my best economy 18.8/gal. Driving 85% Hwy, mostly flat, 50-65 m/h. Very light foot. ECO mode. Hybrid buttery charging very slow. Mostly stays 3-4 bars.
Yes, always premium. Used to run same rout for several years on 2012 XG460 my average was 17.5/gall. No heavy right foot. I suspect something is not programmed correctly.