It goes much faster that way, and then your tiles remain relatively equal thichness edge and center, but that's a minor point. Go to Home Depot, get a 4" closet flange, cast metal variety, and put a pvc short nipple into the threads. Will probably have to get the threaded adapter and glue a piece into it. Makes a good handle. Start with #60 or #80, grind with tool on top. The wets don't last long, and don't overhang more than 1/4". In an hour or so you will be amazed how deep you get. When you get to about 80% of the depth you need, make the tile tool. Continue with the same grit until the curve is out to the edge. Might go to 80 if you started with 60. My 10" was at 120 by the end of the first day using this technique.
Walt