Over the last few weeks I have been monitoring my power meter and my m/kWh, and have concluded the biggest range killer is stop-start traffic. When I'm running "Dad's Taxi" on the same route into town and back at different times of the day, I can see the difference.
Early morning with no traffic and traffic lights on demand, I can keep a constant 30mph with the power meter at 5% or below, using regen to approach the traffic lights until they change and continue without stopping. Doing this, I get 0.1 m/kWh increase every quater mile. (I got over 5 m/kWh last week

)
In stop-start traffic, as I slow down with regen I get back 0.1 - 0.2 m/kWh. However, depending on how quickly I accelerate, I lose 0.2 - 0.3 m/kWh, so never improve the overall efficiency.