Changing Place for Mourning on the Back Bench

During the year of mourning for his father, whose regular place is on the bench farthest from the Ark, does he have the law of changing place?

He must change his place to the side at a distance of four cubits.

Responsa Maharam Shik, Yoreh De'ah, Siman 369: "And it seems to me to explain because it is difficult for me to understand what those sitting in the west will do with those sitting in the east, since a more important place is not considered a change, and if they exchange with those sitting in the east or to the sides, they will be closer to the Ark, and this is considered a change for the better and not considered a change. Therefore, they need to change with their neighbors who also sit in the west. And therefore, the language of the Gemara, those sitting in the north sit in the south, is not necessarily, but to indicate that no change is required for the worse to a place that is closer to the entrance. And from this itself, it is evident that it is not required also outside of four cubits, because what if the synagogue is eight cubits wide. And at least from the language of the author who changed the language of the Gemara and wrote simply that they need to change their place, it is also evident that it is sufficient to change one's designated place. But according to what is written in the book 'Noheg KeTzon Yosef', mentioned above, one should not change to a place closer to the Ark. And so it seems to me according to my humble opinion according to the law."