Where should the Imam stand while leading the funeral prayer of a female or a male?

Narrated Samura bin Jundab

I offered the funeral prayer behind the Prophet for a woman who had died during child-birth and he stood up by the middle of the coffin.

حَدَّثَنَا عِمْرَانُ بْنُ مَيْسَرَةَ، حَدَّثَنَا عَبْدُ الْوَارِثِ، حَدَّثَنَا حُسَيْنٌ، عَنِ ابْنِ بُرَيْدَةَ، حَدَّثَنَا سَمُرَةُ بْنُ جُنْدُبٍ ـ رضى الله عنه ـ قَالَ صَلَّيْتُ وَرَاءَ النَّبِيِّ ﷺ عَلَى امْرَأَةٍ مَاتَتْ فِي نِفَاسِهَا فَقَامَ عَلَيْهَا وَسَطَهَا.