Oriza, no one has replied to you, did you figure this out?
Some other things that might affect your FE are what gas you are using. No one has really uploaded a video of what "ev mode" driving looks like and has just described it, so i will try to get you some video of that in my car.
The dash display could also be wrong, have you calculated your mpg by hand instead since you got the car?
Here is an example of the motor powering the wheels at 45 mph, as well as accelerating in a neighborhood street. Sorry about the dusty car, haven't vacuumed it with the weather being so cold and rainy.
https://www.youtube.com/watch?v=rQAd9bjwue4&feature=youtu.be
https://www.youtube.com/watch?v=xgl8I7Ro3zk&feature=youtu.be