In a Congregational Prayers Muqtadis are not completing the front rows, instead either starts a new row or joins the new row by leaving the space empty in front rows, here the question is whether the prayer of the muqtadi who in completes the front rows will be accepted or not?
Ref. No. 996 Alif
In the name of Allah the Most Gracious the Most Merciful
The answer to your question is as follows:
Making or joining a new row, leaving space in front rows is Makrooh (undesirable); the prayer of the Muqtadis in new row will be Makrooh. But in case the Musallis are not in large number then they can make small rows more than one too.
(And Allah knows best)
Darul Uloom Waqf Deoband