The human body is not completely symmetric.
I often observe in patients that their bronchi is twisted, the vocal folds are not of equal proportion, or the space of the resonance chambers are deformed.
Many people don’t recognize their posture when singing a song. A person’s air passages and breathing have a great impact on the sound they produce. These air passages and the muscles that directly assist their performance can be tight, stiff, or just naturally irregular. Therefore, if you change your posture, you could be able to let air out smoother and increase vibrating the vocal folds to improve your singing. Be mindful of your posture and seek different stances when vocalizing. Such as stretching your neck, putting your shoulders back, or simply just standing or sitting straighter. Sometimes even a small change can make a big difference to your singing. Look in the mirror or record your posture when singing a song. Review your body stance when singing and playing an instrument together or just singing. Everyone has a different style. Do not copy someone else. Please decide what is the best posture to sing a song for you personally.
Note:Conversely, it is possible to obstruct your singing when changing your posture. So carefully review both before and after the posture change to make sure your making positive changes and not negative. In conclusion, it is very important to know your throat and body well when singing.