Is it permissible to place the mihrab in a corner of the mosque, as illustrated in the accompanying diagram?

There is no objection to placing the mihrab anywhere in the mosque (right, center, or left) as long as it points towards the Kaaba. The Imam stands opposite the middle of the row as a matter of preference, not obligation. The purpose of the mihrabs is to indicate the Qibla, and they did not exist during the time of the Prophet, peace and blessings be upon him, but were innovated after him. Ibn Aqil and Ibn al-Jawzi are of the opinion that a mihrab should be adopted for the ignorant to be guided by it. This issue does not warrant dispute and contention.