You do have an excellent grasp on composition already as far as I could tell. Even without reading up on it, most people usually have a good sense of composition even if they can't articulate it.I'm not an expert on composition by any mean, but I've been doing research on a wide range of topics lately.Have you ever heard of the "Ctrl Paint" website? I'm not sure if it might be something that interests you since you're pretty advance as it is. A friend of mine showed it to me recently, and I've been watching some of their video since they cover many topics and seem to be useful regardless of the software or media that is being used. It's something to look into if you're interested in learning more about something relating to art.