Re: E10 all (or mostly) in your head?
My scangauge adjustment is about 5% more gas with e10 vs regular gas, but the mpg is roughly the same. My wife driving the odyssey has about a 3% hit with e10. That's with more miles than what I drive in my civic, and a good but normal driver.
100 mpg commute / 90.2 mpg tank = 1191 miles