Over the course of the game, after practicing, youll get the hang of getting perfects. Also, i believe the higher the level of the ring, the easier it was for me to get achievements, as the area you have to hit gets a tiny bit bigger. Some people say if the ring is a "Ultra" ring, it makes it easier, but i never noticed. By the time you get to the end of disc 4, you should have this achievement. So dont worry about it being un-obtainable.