The majority of the Hanafi, Shafi'i and Hanbali scholars are of the view that it is impermissible to stand in front of the imam during prayer as the rhetoric meaning of the word 'imam' which denotes the spatial relationship between him and the congregation.
The Malikis consider it to be permissible but disliked and should only be done in necessities such as lack of prayer space in the masjid or a latecomer having no space to pray.
The only maintain is to be permissible so long as the person in front can follow the imam's action and the fact that nothing has been mentioned about this matter before. It is therefore excusable if the person doesn't interrupt the prayer by not being able to follow the imam's actions.
The Shafi'i scholar, Ibn Qasem al-Ghazzi, said in Fath Al-Qareeb Al-Mujeeb Sharh Matn Al-Ghaya wa Al-Taqreeb,
"Standing behind the imam in any place in the mosque in such a manner that one is aware of the imam's actions or of those praying in the [previous] rows fulfills the obligation for (following the imam) as long as a person does not stand ahead of him. A prayer is invalid if a person's shoulder extends outward beyond the imam's though there is no harm in standing adjacent to him; it is recommended to stand a little behind."
The author of Mawahib al-Jaleel Sharh Mukhtasar Khaleel cited the following,
"It is doubly disliked for a person to stand ahead of the imam [in a group prayer] or the bier [in a Funeral prayer]: once for standing ahead of the imam and the other for standing ahead of the bier. Based on this, standing ahead of the bier is disliked only, and the prayer is valid whether the person standing ahead is an imam or a follower."
The author of Al-Fawakeh al-Dawani 'ala Risalat ibn abu Zayd al-Qirwani,
"It is known from what we have decided that the order of standing [in a group prayer] behind the imam is recommended; it is disliked to do otherwise just as it is disliked to stand in front of or adjacent to the imam without a necessity."
In al-'Adawi's meta-commentary on Sharh Kifayat al-Talib ar-Rabbani:
"It is permissible and not disliked to stand ahead of the imam during prayer for an excuse such as lack of space in the mosque."
Ruling for a latecomer who finds no space inside the masjid and therefore prays outside:
Stand behind the imam or at least be in line him.
Not stand in front of the imam except when he cannot stand behind or be adjacent to him provided he is able to follow his actions.
Intend to follow the Malikis in this respect.
His prayer will then be valid as is the prayer of a latecomer whom he follows in prayer.
And Allah knows best.
Source: Dar Al-Ifta Fatwa