Is the only available spot in the rightmost part of the first row (adjacent to the wall) better than the empty spots in the leftmost part of the first row that are closer to the Imam?

It is better for the صف (row) to be to the left of the Imam if the right side of the صف is noticeably longer. However, if both sides are equal or the difference is slight, then it is better to align to the right of the Imam.