Obligation of Tzitzit on the Collar of a Sweater or Coat

Is it necessary to round the corners of the collar of a coat or sweater with a high collar, so that the garment has four corners: two at the bottom and two at the top?

Sweaters or coats that are square at the top, a God-fearing person should be stringent and round them. The method of rounding is by cutting the corner in a circle, and it is explained in Menachot 37 and Siman 10, סעיף 3, that folding and sewing in a circle does not help. However, it is explained there in the Beur Halacha that if it is sewn so that the seam is not visible at all, as tailors do, it is effective. If he transfers it to his friend and his friend lends it back to him, there is no need to round it.

The Beit Yosef (end of Siman 10) wrote several reasons to exempt from tzitzit on garments with four corners in front, but these reasons do not apply in our case, and according to him, the aforementioned coat and sweater are obligated in tzitzit. In Darkei Moshe, it is written that they are not obligated in tzitzit because there are not two in front and two in back, and the Magen Avraham wrote, and it is brought by the Mishnah Berurah (Siman 10, סעיף קטן 36), "since this law is unstable in the hands of the Gaonim and they did not find a correct reason (because there are many doubts about the reason of Darkei Moshe, as the Pri Megadim wrote), therefore a God-fearing person should make a round corner, as the Beit Yosef wrote in the name of the elders." And so it is in Ben Ish Chai, Parashat Noach, first year, סעיף 9, and in Kaf HaChaim, Siman 10, אות 23, and according to this, it needs to be examined why on our shirts, which have four corners in front, tzitzit are not placed or the corner is not rounded. The Levush explained that since the collar is folded, it is not considered a corner. The reason why transferring helps is that if it is lent for a day, it is only obligated rabbinically, and regarding this, one can rely on the opinions that since there are not two in front and two in back, it is exempt from tzitzit.