Hi Paul,
Raising the minimum voltage setting on the controller causes the controller to automatically vary the current being drawn in order to prevent the total battery voltage from falling below the controller's set minimum voltage level. This effectively prevents high current being drawn from the battery below the controller's minimum set voltage so that the battery voltage may not fall low enough to cause the
BMS to cut the power completely.
Dependant upon how weak the lowest cell is, it could still cause the
BMS to shut down the power if the single cell's voltage reaches the
BMS's preset limit for the minimum cell voltage.
When the
BMS cuts the power, you usually have to turn the battery Off and On again to reset the
BMS before the motor will restart, whereas the controller simply regulates the power in relation to its own minimum battery voltage setting.
I would also reduce the Max current from 25A to 20A and see how much difference it makes. It is basically a matter of trial and error to determine what settings are best to obtain the maximum range from your particular battery.
Reducing your maximum motor rpm will also extend your range as you will be travelling slower, therefore you will not need to use so much power to overcome the wind resistance, and you should be making life a bit easier for the weak cell.
It is generally accepted that to go twice as fast, you need eight times the power from the motor to overcome the aerodynamic drag at the higher speed.
So theoretically, if you reduced your maximum speed by half, you should travel eight times as far on the same battery, but this might not apply the same at very low speeds.
Although, slight headwinds and tailwinds tend to have quite a noticeable effect on range, even when travelling at low speeds.
More pedal power and less throttle is also very good for extending range.
Alan 
