This is the way I approach props. Every plane, as mentioned is different, and by its design, has a certain speed it wants to fly. The prop has to be able to keep up with the plane, and vice versa. Try to force a "high drag" plane to go faster than it wants, the drag coefficient goes up exponentially and you open up a whole new can of worms. You apparently have a cleaner, lower drag plane, and have been holding it back. Now you are simply letting the plane do what it wants to do. Enjoy it

There is nothing so scientific about this. A prop unloads in flight, but you don't want it to unload to the point where the "plane is pushing the prop" through maneuvers. Any engine is more efficient when the proper load is applied to it. As mentioned, don't underload or overload it.

Having said all that, it's still trial and error from the starting point, you will know when you get it right. You have apparently worked it out just fine, don't mess it up by reading a bunch of prop theory. And I agree with all the other posts above about all the variables.

BO "Your plane is your friend, listen to it. It will tell you what it needs"