This is a good point - it does seem like a somewhat worse result than expected given the stated speeds...this is what I would expect for 80+mph with that vehicle. Assuming it has aero wheels. And no heat use (conditions did not seem cold enough to warrant it and it has a heat pump so it would not be that bad).
I assume you have aero wheels with 18” then? (Looking at your pictures: your avatar of the car says yes. I assume you still have the aeros on the car.)
I do think that your actual efficiency is
perhaps a bit worse than expected. Very hard to gauge that though since it depends so much on conditions and usage and people don’t ever provide every single relevant condition. As
@KenC says: Definitely check your tire inflation and alignment. Perhaps have Tesla look at the alignment, too. That is something they could do - if the toe is too much it could create significant drag, but you would likely see accelerated wear.
Conditions as I see them:
Looks like you had brisk south winds (15-20mph, 30mph gusts) in Austin today, probably as a front moved through, between 9AM and a little after noon. That would have caused poor efficiency both coming and going, given you were traveling somewhat east/west. And if they swung around during your trip they could have hurt you both ways. (I wasn't able to find local climate observation layers through NOAA for your area like I can in most areas. So the details are left to my imagination.)
As you said:
55 degrees on the way out (you should have turned the heat off for this test, probably).
66 degrees on the way back (definitely should have turned the heat off for that).
(To turn the heat off, set the cabin temperature a few degrees below the outside temp, turn off the AC, and turn on recirculated air.)
Even so, with climate control off (or very modest use of heat pump), without winds, at 65mph, I would expect better than 250Wh/mi - I don't have this version of the car with aeros, but my brother does, and he does not have a problem getting ~250Wh/mi traveling at 70-75mph in light traffic without heat use.
Anyway, to me 295Wh/mi seems high, though with a 20mph headwind (doesn't look like you had that, exactly, but I'm not sure), at speeds of 70-80mph to start with, it would be completely reasonable. Headwind hurts a LOT, because it causes the drag force to go up with the square of (vehicle speed + wind speed), and unlike normal ground speed, it doesn't get you there faster (note that Wh/mi has units of force). It's very bad. Nice when it's a tailwind, though it doesn't help as much as it hurts, due to the square factor.