That is excellent mileage while breaking the car in during a cold spell!
May I suggest adding an UltraGauge or ScanGauge?
Then you can block the grill in earnest, as you can monitor air intake and coolant temperature so you'll know when you are overdoing it.
I ran some time with a full lower grill and partial upper grill block. It made the engine run warm, to about 92 degrees Celsius.
The thermostat opens flow to the radiator partially at 80 C, and fully at 90 C.
A severe storm blew away one of my foam pipe insulation tubes and it went down to 80-82 C, and took longer to heat up. FE suffered too.
I now have two clear plastic pieces over my upper grill and the remaining tubes below, now temp hovers just below 90C. FE went up. But I need to block some more
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2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.