EV range in Cold weather

i'm not understanding your question, you haven't posted how much of the beginning range is being used to travel 4km.
if you want heat, or front defrost, the engine has to run.

if you want better mpg's, 4km won't do it in any situation. the plug in was designed so you wouldn't have to waste petrol for short trips.
bundle up, use the seat heaters, clean the windshield manually, and make the trip in ev. it's only 10c, that's nothing!

 

gotcha.

unfortunately, the pip wasn't designed to be used that way, so you're getting the same results as a regular prius would.
it will be better when you don't need heat, but short trips on the engine will always result in low mpgs, it has to go through the warm up process for pollution

 

If you're dressed for winter then maybe try setting it to 17-19 degrees and with aircon off, though I don't know what the humidity is where you are. If the windscreen is fogging up too easily it might just need a good cleaning on the inside (any normal glass cleaner should do). Make sure it's set to auto (it should set flaps to floor/windscreen only when heating) with recirculation off.

Blocking the lower grille (with foam pipe insulation or similar) might help lower fuel consumption, it provides too much cooling to the radiator when the ambient temperature is under around 15 degrees C or so. But as others have said, a short journey with a cold start like this is always going to return poor results.

 

Just start up in hybrid mode and add a shopping side trip to get the engine fully warmed up in the morning.
My winter range is just a few km too short for my daily return trip. I was just starting the motor for one short but steep hill on the morning outward trip.
I recently checked my oil dip stick and it had milky residue from condensation in the engine due to frequent cold starts without thorough warm up.
Now, I make the entire 10 km morning trip purely in hybrid mode to ensure the engine warms thoroughly ... and I can have my aircon running.

 

As others mentioned, the only heat source in the PiP is the gas engine, so if you ask for heat it will run, and you will get terrible fuel economy on a trip that short. Just the way it is.

One other option if you are less concerned about heat and just need to clear your windows would be; when you want to start the car, first press Power without the brake to put the car in accessory mode (not “Ready”), then lower the climate temp to “LO”, then press the brake and start the car. Now you can manually turn up the fan and set the vent to face/windshield and it will blow cool air and (try to) clear your windows.

Won’t heat (and will be less effective than ideal in winter), but can help and not burn gas.

Note that if you press the Auto or Windshield button, it will fire up the engine.

But it is a minor workaround, which needs a bit of planning.

Overall though, best to just drive the already-super-fuel-efficient car and just drive it.