I also noticed that a few places had the midgrade cheaper than the regular.
I noticed that as well .... a lot of the time the midgrade (89 octane) would have 10% ethanol and the 87 octane would not. And then there were times the 87 and 89 octane would have ethanol and premium (91 or 92 octane) would not have ethanol.
I did find that if I kept the speed at or below the magic 3 grand (65 mph) I could maintain mid 30's for mpg.