Ok, had my car for about 2 weeks now. On my second tank of gas. I'm getting around 20 MPG on this second tank according to the dash. The dash also says I've used 12.7 gallons, and that I have about 47 miles to E. Doing the math, that's about a total of 15 gallons, not 16? Is it considered E when there is only one gallon left? Shouldn't it be about 67 miles to E if it had 16 gallons? And I'm sure the tank was full.