Basjoos, while you are of course correct, today I will side with those who will say a factory boattail is, unfortunately, unrealistic. Though a little more effort regarding skirts and a smaller rear end would have been nice.
At least the underside of the car has commendable aerodynamics. Do we have a picture of the diffuser strakes? Perhaps I could imitate their design, now that my underbody is a little smoother.
So the assist gauge goes up to 80kW, but regen tops out at 30kW? Given the vehicle's heavy weight, that's not great. Most drivers won't start braking early enough to get the most regen out of it.
144Wh/mi -> 167mi range on 24KWh.
Can you tell us more about the conditions? Driving style / ambient temperature?
The Leaf uses 250W once booted up. That's only a little more than the Insight draws while just sitting there.