There are many threads on the regen issue on the web but the general consensus seems to be that it doesn't do that much to extend range and certainly effects average speed because in order to get the most out of regen you will be going downhill slower than you are able to go up. It works better in automobiles because they are much heavier.

The surest way to extend range is to pedal along with the motor. I call this staying on top of the motor and you will see what that means when you get to ride one. You just need to find the right gear(s) to do this and as much effort as you want to apply will be repaid in extended range. Doing this I can get 40 miles (64k) out of a 12Ah LiFePO4 battery in hilly terrain without using my regen, although I do use a brushless hub which has a good amount of drag, but the regen is so strong that my setup on a pusher trailer just skids the tire when it is applied. Great for coming to a stop though! Actually I have never used more than 8.2Ah of my battery and have yet to come up against the BMS which is fine with me because the hub motor drag is so bad that although my pusher setup is relatively light it is like riding a resistance trainer and without the assist it would not be fun to drag it home. More likely I would just hide it beside the road and continue on and come back and get it later, or at least that is my backup plan.