For continuous roll receipt-type media and for label media without black marks or notches...
Align the media to the default center position.
For black mark (black line, notches or holes), backed media...
Adjust the sensor position in such a way that the sensor aligns to the center of the black mark.
Avoid the center area of the media so you only use black-mark sensing for printing on black mark media.
Web (gap) sensing standard operating position for the sensor (default)
Off-center sensor position (use for black mark sensing only