This is right from energy.gov

https://www.energy.gov/eere/amo/articles/determining-electric-motor-load-and-efficiency

Most electric motors are designed to run at 50% to 100% of rated load. Maximum efficiency is usually near 75% of rated load. Thus, a 10 horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp.

They also run more poorly below 50%.

To get a good city/highway range they would need to try and keep the motor above 50% for city, while also keeping it under around 75% for highway. How you move that gearing will impact range at higher speeds or lower speeds. Maybe it's not as much as I think, but it definitely comes into play, and the Taycans geared motor helps some amount.

Tesla has definitely honed their motors to maximize the EPA range vs higher speeds in addition they aren't de-rating like some other manufactures do.