And, that said, tongue arch might work to make the resonant chamber in your mouth smaller. Any "air stream" explanation is complete nonsense. (I would have rather used a different word).
The air has one job and one job only to excite the vibration. People just do not realize that not only is the mouthpiece and the horn a resonant system, it also includes your oral cavity, your throat, and your lungs. Sitting up and taking a big breath opens up those resonant cavities.