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

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

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':

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.