إِذَا لَمْ يَكُنْ مُقَابِلُهُ مَنْ قَدْ فَاتَهُ بَعْضُ صَلَاةِ الْإِمَامِ فَيَكُونَ مُقَابِلَ الْإِمَامِ إِذَا قَامَ يَقْضِي.
While there is no such person in front of him whose some part of the prayer has been missed with the imam. Therefore, when he stands up to complete his prayer, he will be in front of the imam.