I found an interesting drill yesterday. I played the mouthpiece from the other size like a mini trumpet, i.e. put the shaft inside the mouth. It did not make any sound initially. But when I reduced the amount of air exhaled, it whispered at a soft C note. It seems to be a way to practice passive reduction. That means very little air is required to play note C. It also imitated the opening required to allow free throw of air. I don’t know whether it is a good way or a wrong way to find the shape. Hope I could receive some feedback on this finding.