Yes, 270 Wh/mi is a bit high for SR+. EPA estimate for the SR+ is ~250 Wh/mi for 45% highway, 55% city driving.
If you're mechanically inclined, you can work through some of this like you would for a traditional ICE car that's not getting the fuel efficiency it's supposed to; just skip past the mechanical items an EV doesn't have. Even if you're not mechanically inclined, check the stuff you're willing and able to and then if needed, take it to a service center (ideal) or garage and ask them to look into it for you. Here are some potential reasons for poor fuel efficiency I can remember off the top of my head.
- Anything that adds to rolling resistance. For example, an intermittent sticking brake caliper; this would cause a brake pad to stay applied even when the car is not braking. Severely underinflated tires. Regularly carrying a LOT of excess cargo weight or carpooling with a full load of adults; especially if everyone is circumferentially challenged.
- Engine/drivetrain issues. In ICE cars these include spark, fuel, air, exhaust, and issues that prevent the engine from operating at its designed operating temp; ask a EV tech for EV specific mechanical causes. I suspect operating engine temp and operating battery temp would be included in items an EV tech would want to check.
- Driving style. This matters most in city and/or stop and go traffic; the more highway driving you do at uninterrupted speed the less impact this has because the frequency of gunning it would go down. Although all vehicles (ICE, EV, fuel cell) are less efficient at very high speed than at their optimum 45-55 mph.
Try doing an unscientific test. Drive 5 miles away from home on city streets and come back along that same route (this will zero out any elevation gain or loss driving away from home). What's your Wh/mi for that 10 mile trip? Drive 5 miles or so on a highway at a steady speed (no speeding please for this test) and come back on the same highway for the same distance. What's your Wh/mi for that 10 mile trip? You could even test your driving style against someone else's by having both of you drive the same route and comparing Wh/mi for each driver.
If you care to know, our SR+ has roughly 18k miles and a lifetime 230 Wh/mi history. We've driven through mountains, short trips, multi-thousand mile road trips, and live where overnight freezing temps are common in the winter and the inefficient heater has to work hard for 4-5 months of the year.
The resistance heater in the TM3 really affects Wh/mi. San Diego is in climate zone 3B, meaning the heating needed is far less over the year than throughout most of the continental U.S and shouldn't negatively skew your lifetime Wh/mi.
Good luck.