10-12 miles, if you can go 40 miles per hour or less is ideal for this car.
The first 2-3 miles will be warm-up and you will get ~25 MPG.

The last 7-10 miles, if you utilize all the "hybrid" features and get that engine off and use the battery as much as possible, will get you 40-50 MPG.

2-3 mile trips are the only "killers" to MPG. More than that, and this car does awesome. I did a "cold start" at 11 degrees last night, just to take movies back to the rental store.

3 miles out - no EV, and I got 25 MPG.
3 miles home - EV most of the way, and I got 45 MPG.

6 Mile AVE. = 32.1 MPG @ 11'F

If my trip was longer, I would have crept closer and closer to the 45 MPG mark. Speeds were in the zero to 40 miles per hour range.

-John