If you clean the hole and get the shim feathers to seat on their shoulders, with the Chinese with rubber bands, and hit the plug wedges square, less breakage with tools. Plus the rubber band helps keep them together and less lose of tools. We drill down both sides when the stone is thicker, scoring 1/8” down with 4” grinder will straighten the crack. Keeping all the drilled holes in a single plane also improves the edge created. The shorter you drill the holes, not only will it save money by saving bits, but make it easier to chip off the half a hole if needed to make customers happy