I just grind the overhang down in the melamine form with a cup wheel. when I have the piece on my cart I hit the edge diagonally with my 200 grit wet polisher....just two passes on the edge and done.
I use Knife Edges whenever I can. I'll tape off the top of my mold wall. Spray, then pull the tape. Then I spray my taped off Knfe Edges and screw them onto the predrilled mold walls. Then hand pack my apron and make sure to press the backer up into the corner. Then just knock down the hard corner w/ a bit of polishing. This has saved me a HUGE amount of grinding. I still grind for a lot if a knife edge wont work. It also helps to give me a gauge for my drop edge thickness as well a protected cap to screed against.
Below is a flat grinding disc that works extremely well for cleaning up the back sides. The diamonds wrap around the disc so it can cut and grind.