The working of potentiometer is based on the fact that the fall of potential across any portion of the wire is directly proportional to the length of that portion provided the wire is of uniform area of cross-section and a constant current is flowing through it.

To shift the balance point on the higher length, the potential gradient of the wire is to be decreased.  The same can be obtained by decreasing the main current, which is possible by increasing the resistance in series of potentiometer wire.