I have a very similar situation myself with my HCH-I as far as commute. From a cold start, I go up 150', then back downhill about 700' to the freeway, in slightly under two miles.

At one point, I actually tested what the idle fuel consumption was of the engine warmed up -- it appears to be around 0.1 gallons per hour. I figured this out by allowing the car to coast up to speed until the moment the instant MPG bar "maxed out" at 120 mpg, which occurred at around 12 miles per hour (1 gallon in 10 hours). Idle fuel consumption when the engine is just still warming up appears to be about three times as much. A 3000RPM, 8% climb is probably around 17mpg @ 30mph, or 1.8 gallons/hour.

I don't believe that the indicated numbers you just gave can possibly be right however, as I have never seen such a drastic fuel consumption from cold start. The total "downhill" mileage for me (including the initial 150' uphill immediately after startup, and the fuel I burn accelerating from stopsigns) ALWAYS brings up my tank average, even if only slightly.