I don't know if you are right or not, only that this is one of the most discussed topics ever. All we know for sure is the electronic display is not good for very short segments, but pretty good for tank averages. Mine ( and most ) tend to read 1-2 MPG higher than actual.

Also, your gas tank holds a "nominal" 15 gallons. However, there is 3 gallons of "air space" in there. So, you can actually pump in much more than 15.0 gallons. No matter how hard you try, you cannot replace exactly how much you burnt on the last tank. For this reason, most people trust the gauge for single tank approximations. The BEST idea is to track multiple tanks. GreenHybird is a great place to do that.

I KNOW my car is getting 37.4 MPG overall.
I think it got about 33.1 mpg last tank.
Does that make sense?
-John