To many variables to accurately measure "break-in" on mpg. -driver training (very big one" -traffic -weather -seasonal gasoline changes -whether SWMBO is complaining about driver technique. (Speed uo, slow down, why coasting from block away from light Etc, etc.
Welcome to the car where you can get 45 mpg and still be a little disappointed If you have stop lights, need to accelerate rapidly and go 75 mph, 45 mpg may be as good as it gets.