Is there a text or evidence that differentiates between the regular Imam and the non-regular Imam regarding the issue of catching the first congregation by the Tashahhud when there is a second congregation present?

The issue mentioned is one of the matters of ijtihad (definition) (independent reasoning) that scholars have deduced from general texts and Islamic legal principles. Sheikh al-Islam Ibn Taymiyyah elaborated on this matter, holding that it is better for someone who caught less than a rak'ah to pray another complete congregational prayer, because catching the congregation from the beginning is superior. If one caught a rak'ah or less, and we say that he caught the congregation, his catching this congregation might conflict with his catching the second congregation from its beginning, and catching the congregation from its beginning is superior. If both congregations are equal, then the second is better. But if the first congregation is distinguished by the perfection of its virtue, or the large number of worshippers, or the excellence of the imam, or because it is a regular congregational prayer, then it is better from this aspect. Sometimes one might be preferred, and sometimes the other. And his praying with the regular imam in the mosque in congregation, even if only one rak'ah, is better than his praying at home, even in congregation.