using a new cutter is the trick. a little smear of paint thinner on the glass n run the wheel at a steady rate with gentle but sure preasure. you'll hear that distinct sound as the glass micro fractures under the wheel. work on a hard clean surface. cut first surface mirror from the back side, not the silvered side.
with practice, you can remove slivers as small as 1\16". its just a feel for the material n tool. to take that small pice off, use special glass running pliers or drop jaw pliers.
an easy way to remove small amounts of glass to size it, use a fine emery cloth. i use a belt sander but you can just do without, just takes longer n a bit of elbow grease.
*caution... wear eye protection