Howdy,
You should be able able to use your right hand to feel for the leak. Move your hand to the lips on the right side. Where precisely is the air coming from? You may not having enough tension in your mouth corners that extends along the lips to the aperture corners.

Go back to Greg’s “The Mouthpiece Revisited”. Do all the release activities with tissue, the fingers, the visualizer, and the mouthpiece. Do you feel a leak when doing these? How about with the leadpipe?

Let us know what you find out? Someone here will have an answer or you will discover it.

Cheers,
Ronald