Obtaining optimal matching threshold and finger positioning on scanner

The current matching threshold as per Libfprint SDK documentation, is 40, 40 being an integer and not a percentage . However during an initial test we came across one case of a false positive, so a need arose to alter the current threshold to an optimal value as well identifying the best position to place the finger while enrolling and matching the patient. we are also yet to identify if the design of the scanner may also have an effect on generating a clear template from the fingerprint image