Basically everything has already been answered above...
LR RWD vs. P3D+:
AWD & P3D are less efficient; LR range is actually truly ~340 miles as mentioned, whereas AWD is really close to ~310 miles, driven efficiently. This is due to inefficiency of front motor (it's an AC motor which is less efficient that the rear motor) and additional losses of having to coast that motor & spin the axles & other drivetrain components, even if it isn't really being used.
P3D+ Tires -> as people have mentioned. This is one primary factor, and it's huge. It takes you down from the 310 achievable with the AWD to probably something closer to 270 miles best case (see the tables linked to above, though they are just estimates).
Weather -> You've been dealing with cooler temps, so the heater is getting used, as compared to the summer you dealt with previously in your RWD. AC is a LOT more efficient than the heater (because A/C is a reverse heat pump). For perspective, without solar heating, the heater uses about 2kW when heating interior to 70 degrees with outside temperature of 60 degrees. And that's AFTER the interior warms up. Initially the heater can use over 10kW! If it takes 5 minutes to warm up, that could be perhaps 500-800Wh of battery use (distribute that over the length of your drive...in addition to the steady-state use). As mentioned, rain makes it even worse. Usually in LA "cold" and rain come hand in hand...
For me, in P3D+, I am very gentle with the cabin heat, drive efficiently (mostly), and I'm averaging 300Wh/mi over 900 miles. Depending on whether you're dealing with hills (I have some and due to energy "slosh" they will result in lower efficiency than perfectly flat driving, even if net elevation gain is 0), I don't think you're likely to see much better than that for day-to-day runs. For a longer, conservative drive (limit top speed, modest drafting off traffic, no heat!), you can probably get closer to 270Wh/mi (would give about 275 miles range).
I've been told the numbers will come down a LITTLE when the tires become slightly more flexible with use (lowers rolling resistance), after around 1k miles. But I think this is likely to be a very small change, and totally insignificant compared to the other factors. For me the Wh/mi usage has been going up over the first 1000 miles, as the temperatures have come down.
As suggested, if you get a set of 18" wheels that fit your calipers & have the correct offset for the brake rotors, the MXM4 tires will allow you to hit nearly 310 miles (but still won't be as good as your RWD was - and you won't be able to use aeros), if you're not using climate control and driving efficiently. Might be a good idea for road trips, but it has a significant negative effect on your braking distance & handling.
