The pneumatic application of texture requires that you thin to achieve finer spray patterns, and leave it thick to have bigger particles. Topping coat is a finer and more thinned version of general purpose compound. I have found even topping coat requires additional thinning to spray. It takes some experimentation. I usually start with premixed “ready spray” texture, and will thin as needed.
It is critical to allow the texture to remain on the surface long enough to begin to setup before doing the knockdown, or you lose definition of the spray particles and end up with a skim coat. Keep in mind this texture is water soluble so mistakes can be fixed, and you need to prime to protect it when finished.