MPG Calculations

I understand that the computer generated MPG readings are optimistic. There are times, particularly when going downhill that I can adjust the throttle to obtain the theoretical 100 MPG. At that point I can lighten up on the throttle a bit more and move the Hybrid Systems Indicator bar graph more to the left. I wonder when running it further to the left while showing 100 MPG on the bar vertical bar graph if the computer is using better than 100 MPG in its calculations? In other words other moving the graph to the point where the battery is being charged, is it best to strive for the lowest Hybrid Systems Indicator level to increase the calculated MPG, which must be greater than 100 MPG?

 

Thanks for the responses.