Can I suggest yu use a ScanGauge II. It is a combination
Scantool and
Gauge set. Very small and plugs into the OBDII port under your dash. $160
The display can mount on your steering column. Like mine. It installs in minutes, literally.
It will give yu the MPG , trip info, etc, all the info. you want and more!
I have an 06 Highlander LTD. with Navigation. I agree that the way Toyota displays MPG is rediculous. My OE display shows a similar MPG layout to yours. And I think it is dumb of Toyota almost to the point of being insulting to us as Toyota owners.
ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool
For the price ,yu really get alot of bang for the buck.
Just my thoughts
LifeTech