If you press the mouth of the hose and control the pressure, you can make the water splash strongly and reach far.
The similar phenomenon is observed when pumping the air out; the point is to give a certain pressure.
With this point in mind, try to vocalize, pushing the inhaled air strong against the deep upper palate, the upper part of the throat with sufficient abdominal pressure, and manipulate the tone by narrowing the gathered part.
The trainees with advanced techniques of vocalization may understand the knack of making the voice higher.
Relating to this, I have advocated the inclusion of singing to vocal training. Songs are composed of high tones and low tones in a rhythm. This will naturally train the stressing and relaxing of the muscles of the gathered part, and leads to the progress of the speech, and high tone will be enforced.
