Shaikh Abdul-Muhsin Al-Abbaad was asked the following question:
What is the ruling on specifying a prayer mat for the Imam of the masjid in addition to the carpet of the masjid?
There is no need to increase upon the carpet of the masjid. Not for the Imam or other than him.
[Sharh Saheeh al-Bukhari no. 59 Side A]
Faisal Ibn Abdul Qaadir Ibn Hassan