As a newer insight owner I am in a different boat, sort of. The t stat seems to open around 180, the electric fan kicks on at 205 and about 188+ the engine starts to retard timing and upping the cvt ratio.
Having said all that the more of the grill you block the better the mpg is and accleeration in the 60-70 range.
Having said that x2,
I try to find a happy medium where the car doesnt run the radiator fan and the temp stays below 200 degrees under acceleration, merging onto the interstate, yet doesnt fall below 180 cruzing.
With that being said I find if I use the ac I block the upper grill and leave half the lower open. In the weather where it may reach a high of 60 with a low of 30 I block all but an inch by 3 and leave the heater on low. If the car gets warm inside Ill crack the window and leave the heat set at 85 degrees. Any more and it will not do the fuel cut off thing or enter ev mode under extreme light loads.
Running the half block of the lower grill I was seeing 175 the past week with this colder weather since the hurricane passed through.