That method is sound. I made a science project with my son that showed reflection angles. We took 2 points and put nails in them then took a loop of string larger than the 2 points and looped it around them. Took a sharpie and stretched the loop taught on both of the nails to make a triangle and continued to draw the oval with the sharpie so it was an oval around the 2 points. We then put a 1" border following the oval line and lined it with reflective foil. Took a laser pointer and set the tip on one of the nail points and wherever you pointed the laser pointer within the oval, The reflection would pass over the other point. Got the idea from an oval pool table demonstration with 2 balls on the points: wherever you hit one of the balls, it will bounce back and hit the other ball minus and english you put on it.
