How about this??!!
At half tank, 284mi (I should mention that I had to reset the trip after 13mi) and OBC reading of 30.9mpg
Full tank = 16.6gal
Half tank = 8.3gal
Calculated MPG: (284+13)mi/8.3gal = 35.8mpg!

I know... it's a bit more than Half tank, but so what. I still think it's impressive.
Dough