Question about mpg readout on the screen

We've only had the car for a week but I'm puzzled by what I'm seeing for the mpg on the screen. At no time has the screen indicated an average mpg of outside the range of 44.7 to 45.0 mpg. This is despite filling it up, resetting the trip meters and immediately heading up the Cajon Pass twice while the instant fuel economy indicated 25 mpg or less. I understand the inconsistency of calculating at the pump because of the bladder but doing that has worked out to 2 fills in the high 30s, one in the high 40s and one of 53 mpg. Yet the car still reads 44.7 to 45.0.
It's not a big thing because I don't depend on it; I tend to fill the car when it goes below 1/2 full and over time I will have enough pump calculations to give me a fairly accurate depiction of my average mpg.

What would cause the screen to read in that 44.7 to 45.0 range when it is obviously incorrect?

 

Thank you! I feel like an idiot for missing it when it's right there in plain sight. I guess I'm expecting everything to be more difficult and complicated so I'm overlooking the obvious and the simple. The learning curve continues.....