That makes me wonder if speed is weighted more heavily than terrain in the GOM algorithm. It may not be a direct calculation based on overall miles / kWh efficiency.Cool post! Thanks.
It must not be linear. I get an average of 4 miles/kwh and my 87% charge range is ~207 miles in my new 2021 Bolt. About 2-3 weeks ago, it used to predict ~225 at 87%. And when I bought it a month ago, it was ~259 at full charge. My current 87% range seems low but I guess it's the GOM. I will play with OBD2 to see if a cell went bad or something... but I'm guessing it's not linear (i.e. it's not simply 259*0.87 for SOC and rated milage nor is it simply 4*65*0.87 for average miles/kwh, 65kwh battery and SOC, etc...).
However, I do a lot of 70+ mph highway driving. My 4 miles/kwh comes from going downhill to work one way and uphill the other... all the while going 70+ mph mostly both ways. It somehow averages out to 4 miles/kwh though!
Also, is your auto-defog setting turned on or off? As the weather gets warmer or more humid, auto defog may run more and impact your GOM. I've noticed that simply turning on the A/C or heater will immediately affect my GOM, regardless of my miles / kWh efficiency at the time.