In fact, vocal music is not as complicated as you think. You should not deliberately think about how your chin should be or how your articulation should be. In fact, vocal music is based on speaking and adding a high position. When singing, the shape of the mouth should be as round as possible. You can feel the feeling of yawning and recite based on the feeling of yawning. Gradually you will find this feeling.

Theoretically speaking, the upper jaw is too high and the tongue should be flat so that the jaw does not exert too much force. You can take a mirror and look at it. The key is to find that feeling. I wish you success!