When "Regular" isn't the cheapest gas..

I report the prices **as posted** on the signs at the stations. The Ayerco 66 at 5th and Stanford is on my way to and from work so I post it often. I called Ayerco in Quincy and asked why "Regular" is 5 cents more expensive than "Plus". Their answer is that the "Regular" grade gas they sell there contains no ethanol and does not get the same tax break, but since it's 100% gasoline, which has a higher energy density than ethanol, it also gets better gas mileage so it's still more cost effective than the "Plus" grade which is 5 cents cheaper.

It has been suggested that the cheapest price be reported as "Regular" regardless of what the actual grade is. I've been around the journalism trade long enough to think that is not correct. Reporting is reporting and should be accurate. Whether many people buy the "Plus" grade since it's the least expensive at the station in question, is not relevant. If the station calls it "Plus", then, to me, it's not "Regular" as they have another gasoline grade that they designate as "Regular".

Am I wrong to try to be accurate? Comments?