Q. (See question 2309 above). One who is used to blow a wind musical instrument and does so in many simches. Can he blow the shofar with the middle of his mouth, as he does lehavdil, with a trumpet since he finds it easier?
A. As mentioned above it is preferable to blow with the right side of the mouth and with the righr side of the mouth, as it protects the side that needs protection from evil spirits and is also not protected by the tefilin. But as we mentioned above, most Poskim also agree that in need he may use the side he feels most comfortable with. so he may blow easier and better. (Piskei Teshuvos ibid. 5). This likely would include blowing with the middle of the mouth.
Horav Shlomo Miller’s Shlit’a opinion is that he may blow from the middle of his mouth if he blows easier and better, but he should slightly move a bit to the right.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a