Why is irji3oo; in surah yusuf ayah 81 read with tafkheem (some call it full mouth)?

Question
Why is irji3oo; in surah yusuf ayah 81 read with tafkheem (some call it full mouth)?
Answer
Bismillah Ar-Rahmaan ar-Raheem
There are 8 cases in which the letter ra' has tafkheem.  The rule of the ra' saakinah preceded by a hamzah al-wasl is number seven in the following link showing the rules of tafkheem for the ra':
http://www.abouttajweed.com/index.php/tajweed-rules/53-tafkheem-and-tarqeeq/59-tafkheem-and-tarqeeq-part-3
The word has a ra' saakinah preceded by a hamzah al-wasl.  Whenever this happens, the ra' is read with tafkheem. We do not look at any other reasons when the ra' saakinah is preceded by a hamzah al-wasl.