Setting aside
all the heating problems I've had with my car since Thanksgiving, I've found, especially in 9F weather here in NM, that it pays to take a half-hour or even an hour to heat the car before driving. (My car's heater is extreeeeeeeeeemely slow at getting heat going... pumps out cold air for a long time before warming up.) In the bitter cold mornings I'd turn the heater on, temp set to HI, and let it just blow into the cabin while car's parked in garage for a good lonnnnnnng time, while plugged into the HPWC. The car senses it's plugged in, so it draws from the grid rather than the battery. This really saves on Wh/mi numbers once I'm rolling.
I also tend to go overboard in terms of preserving battery, at the expense of comfort, so once rolling I tend to turn the heat OFF, and then set the driver's seat to 3, then after 5 min, 2, then after a few more min 1. Keeps things tolerable for maybe 20 min, after which time I turn the heat on HI and full for a few mins to warm things up again. Then shut 'em all down and repeat the process. This keeps the Wh/mi to more reasonable levels. If I don't do this, I see high 400 Wh/mi numbers pretty quickly. Sometimes into the 500s. And I have an S85.