How are the rows arranged behind the Imam, starting from the middle or from the right in the first row and subsequent rows?

The Sunnah is for the Imam to stand in the middle of the row, then the row begins directly behind the Imam, and is completed to the right and left. There is no harm if the right side is slightly more than the left. This is indicated by authentic Ahadith, in addition to the sayings of scholars that affirm the desirability of the Imam standing in the middle and the rows being filled first and foremost. The right side of the row is preferred over its left, unless that leads to a noticeable gap.