How bad is your MPG in the winter time with short trips?

that sounds about the same as i get with mine

 

I bet you're running the heater, too. This effectively establishes the least efficient set of parameters for Prius operation. I'm surprised you're getting as many MPG as you are. When you ask for heat, the ECU runs the engine constantly to get the coolant temperature up. But since the heater core is effectively another radiator, you'll never get the engine up to temperature. Then the ECU runs extra fuel into your (relatively) cold engine, acting like the choke would on a car with a carburetor. Under these circumstances, 30 MPG seems on the high end of what you might expect.

 

This is the only thing in your list that stands out to me.

Try running your tires at recommended pressure + 1 PSI, so that would be 36 PSI Front / 34 PSI rear. It might not make that much of a difference, but it should help a little. at least 2-3 MPG.

What altitude are you at, and what grade (octane rating) fuel are you using?

 

Why Mileage Gets Worse in the Winter | PriusChat

Do you have snow or other precipitation on the ground? This compounds the normal winter losses.

It will depend on your driving profile, outside weather, and cabin heat conditions, not just the thermostat suitability.

Have you tried a grill block to retain more engine heat? Or a block heater to pre-warm the engine?

 

This.
I rad block my Gen3 and and my "c" (essentially Gen2 engine) for 5 years now and also just
installed engine block heater.] a month ago.

My Gen3 gets a 1.2 miles round trip 3 times a day (kiddies to school, and one in kindergarden/half day)
My "c" gets a 3 miles each way commute to work.

Engine block heater has raised coolant temps about 30-40f after 1.5-2 hours
and results have been about 5+mpg for the larger gen3 and a good 10mpg gain roughly for my "c"
So my "c" has been getting very close to 50mpg still in 30f temps similar to summer mpg.

ymmv