Distance factor is used by a 3D listener to define how many meters each distance unit represents. Thus if your application wishes to use a different scale, just set the distance factor to the number of meters per distance unit of the desired scale.
For example: if you wished to use feet as your distance unit, you would set the distance factor to 0.3048, which is the number of feet in a meter.
Changing the distance factor will primarily affect Doppler calculations.