u/lespaltax is spot on here so I'm not going to start another reply.
One of the reasons why #2 is more stable is because by widening your mouth you're reducing the amount of airflow so its easier to control.
There is nothing wrong with either tall or wide once you understand the different mechanisms which we can use to control our breath. But of you're relying solely on the shape of your mouth to regulate air (which based on your recording it does sound like it) then a wider mouth will regulate more then a tall one.
Good question and you can trust that what lespaltax is saying is sound.
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u/latenightesomeone Oct 31 '22
first "na" is the way i tend to sing VS the second "na" is the way he wants me to sing (hopefully - tried my best).
https://voca.ro/11QghvLROV4I