When we talk about different prop sizes for planes we are working within the engines rpm range too. By changing lengths and pitch it effects how well the engine pulls the plane. The manufacture of the engines gives us a starting point of sizes then we test different pitches and lengths to decide what prop works best for the plane/engine combo. Going too small takes the engine over it's working rpm range, too big and it lugs the engine down too much. This is what you will see when plane guys are talking about prop sizes. A 10 inch prop with the small pitch on a .55 engine could over rev it and cause problems. Running more blades like you are can compensate for a bigger prop. Check to see what rpms your engine is running just to be safe.