285exp

I don't think you're seeing what you think you do. The first time I ran the premium test was 3/25/2013 - 5/9/2013, the average mpg for that 1215 miles was 21.2mpg. The previous 4 tanks, excluding one because it had significantly more highway miles and wasn't representative of my normal driving, was 1188 miles at 20.7mpg. The 4 tanks of regular following went 1226 miles at 20.6 mpg. The average of the 4 tanks before and the 4 tanks after the test was 20.64 mpg Overall, using premium increased fuel economy by 2.6%.

The non-ethanol fuel test went from 8/27/2014 - 10/20/2014, the 4 tanks of E0 on my usual commute went for 1189 miles and 21.2mpg. The average for the 4 tanks of E10 preceding and the 4 tanks following the test was 20.7 mpg, for an increase in mpg of 2% by using E0. As a bonus, I made a long road trip of 420 miles on the last tank of E0, average trip speed of 60 mph, and got 30 mpg. A few weeks later I made that same trip, using E10, and got 29 mpg, so I saw an increase of 3.3% by using E0, almost exactly what is predicted by the loss in energy content in E10.

In both cases, a small increase in mpg, but not enough to offset the increase in price.