Which positions are best in the row behind the imam?

Question:
If a person arrives and the first row is empty, which is better: to be directly behind the imam, slightly to the right, or to the left?

Answer:
If he is directly behind him, that is the head of the row. If he is to the right, the right is better. As for being directly behind him, he is in the middle. It appears that the best position is directly behind the imam, because he has secured the foremost position, the head of the row.
Q: If he is at the far right, and to his left is an elderly man praying while sitting, and when the prayer began a gap was found between him and the rest of the rows, should he leave the elderly man and complete the row, or form a group with him?
A: The first row is better, and the right side of every row is better.
Q: When the rows became aligned, a gap appeared between him and the man?
A: He should fill the gap.
Q: Should he leave the man to pray alone?
A: He should ask him to move closer to fill the gap.