A person was not sure whether he was in front of the imaam. What is the ruling?

If a member of the congregation is not sure whether the place where he was standing was in front of the imaam or not, what is the ruling in this case?

Praise be to Allah, and blessings and peace be upon the Messenger of Allah:

His prayer is valid, as was stated by al-Shaafa’i. This applies whether he was further ahead of the imaam or behind him.

From Fatawa al-Imam al-Nawawi, p. 58.

But it is not permissible to deliberately stand in a place in front of the imaam. And Allaah knows best.