Question:

Due to lack of space in a train, can an Imam stand between two seats and the muqtadi (follower) stand directly behind him? Or would it be better to perform salah individually?

Answer: حامدا ومصليا ومسلما

The salah will be valid. You should not perform the salah individually, rather perform it in congregation. Once there is a valid (shar’ee) excuse, then there is no problem for a man to stand alone behind the Imam.

لان قيام الواحد خلف الامام مكروه تنزيها كما صرح في الدر 1:419 على هامش الشامي

And Allah Ta’aalaa knows best.
Hazrat Mufti Ahmad Khanpuri Saheb (May Allah preserve him)
Mahmoodul Fataawaa 1/442