The recommended CG aft limit is usually quite a bit forward of the true aft limit - where the airplane becomes dynamically unstable in pitch - a no-fun situation. I have one only test for CG for aerobatic airplanes. I trim the airplane to fly straight and level, then roll it inverted. If it is nose-heavy, it will take a fair bit of down elevator to prevent the nose from dropping, while inverted. If it takes just a touch of down elevator input, the CG is probably close to ideal. If the model climbs with hands off the elevator stick, it is tail-heavy. I like to slowly move the CG aft, carefully evaluating performance at each step. As the CG moves aft, you have to reduce elevator travel to keep the same pitch rate. A lot of people seem to omit this step, and get scared off by the increased sensitivity to elevator input. Some models will be happy with the cg far enough aft that they will fly level both upright and inverted without retrimming the elevators, but most tend to get a bit cantankerous in pitch before their CG is this far aft.

Trainers, of course, need a rather nose-heavy CG to give dynamic pitch stability, but this is no good for top-level aerobatics, where you want the airplane to hold any line, hands off, as far as possible.