I'm getting very good mileage in my HCH in part due to previous experience driving for mileage but mostly due to local conditions. I've got it better than most but believe it or not it could be a lot better. The wind makes a big difference in mileage and going to work the drive is into the wind (most days), this drive occurs during the day when the wind is stronger. Coming home at night is with the wind but the wind does not blow as hard at night. The net effect is like driving into about a 5mph head wind all the time. The hillyness of the area does not help and it could be warmer as well.

I shouldn't complain because the advantages out weigh the disadvantages. Working second shift cuts traffic down a bunch especially at night coming home. The commute is about the perfect distance at 30 minutes. Any shorter and the car would spend a higher percentage of the time not warmed up. If the drive was longer I'd get impatient and speed up to save time. The weather is pretty good over all but AC is still required in summer and we get ice and snow in the winter. The speed limits and traffic allow for a nice 40-45mph speed for most of the trip. There are a few stop signs and traffic lights but plenty of places to cruise for a while without needing to stop.

If a second shift hypermiler lived somewhere that was warm, dry, flat, and if they lived on the windward side of work (instead of leeward like I do), and if they had a more nonstop trip to work they could be averaging in the high 60's or maybe even low 70's with a Civic!

Your insights into the effect of local conditions on mileage are important!
I live in Galveston on the TX coast, and have noticed that quite consistently my mileage driving from Galveston into Houston (hwy, about 70-75 mph) is much higher (about 52-55 mpg) than returning to Galveston (about 42-44). It is a flat highway, and the only explanation I can come up with is the tailwinds (from the coast) vs headwinds (going back South), I just never though the difference would be so pronounced!
One other interesting observation I made during driving in the TX hill country (North of San Antonio): I made multiple back and forth trips from Fredericksburg to Enchanted Rock State Park. It's about a 15 mile trip over very hilly terrain (with many quite steep but short inclines), with an elevation gain from F'burg to E'rock. However, the gain had far less of an effect than the speed, and the effect was quite paradoxic. When driving near the limit of 50mph, I averaged only about 45 mpg, both ways (average was there and back to eliminate effects of elevation changes). However, when driving 65mph, I averaged about 57 mpg! The best single trip averaged 64 mpg at speeds of 65-70 mph!
I was pusszled by this, but believe there is a sweet spot in terms of driving speed, in relation to the efficiency of HSD. Obviously at higher speeds the drag increases consumption. However, at slow speeds (below 50), the HSD 'labors' up the steep inclines with very low instantaneous mileage (in the low to mid teens), while at a high average speed I can almost coast up the inclines and gently accelerate down the other hill, with the instantaneous mileage on up- and downhill never dropping below 50!
That basically tells me that while in general higher speeds are bad for mileage, each set of driving conditions have a 'sweet speed' (for lack of a better term) that might be best for maximizing mileage. The otherinteresting thing to note is that when averaging close to 70 on these hilly roads, my mileage was well above 50 and closer to 60 mpg, while driving at similar speeds on a completely flat highay, I can only rarely (with tail wind) exceed 50 mpg.
So, hills ain't that bad folks!
Find your sweet speed!