In Arabic loanwords, why does Persian change the short vowels with different vowels instead of matching them with long counterparts?

Question

Classical Arabic (4th-9th century) short vowels are /a/, /u/, and /i/, and long vowels are /a:/, /u:/, and /i:/.

New Persian (1000-1200 years old) short vowels are /æ/, /o/, and /e/, and long vowels are /ɒ:/, /u:/, and /i:/

Orthographically speaking, /æ/ in Persian is written like /a/ in Arabic, /o/ like /u/, and /e/ like /i/. The same goes for the long vowels; /ɒ:/ for /a:/, /u:/ for /u:/, and /i:/ for /i:/

In Arabic loanwords in Persian, like kitaab/ketaab (written exactly the same way in Arabic and Persian, even with diacritics), which is a loanword from Arabic, why is it pronounced as /ketɒ:b/ in Persian, when it would make more sense for it to be pronounced as /ki:tɒ:b/, since I would assume /i:/ is closer to /i/ than /e/? In other words, why was the Arabic /i/ transferred to Persian as /e/ instead of /i:/?

Similar changes also apply to other words borrowed from Arabic. Few examples:

• imtiħaan/emtehaan "test"
• istiʕmaar/esteʔmaar "conquest/occupation"
• sulħ/solh "peace"

Answer 1

I see evidence that this is just some relatively modern shift in pronunciation in Persian in some accents.

For example, i in the pronunciation of kitab is preserved in 1) the languages which inherited the word from earlier Persian (Turkish, Azeri, Kazakh, Pashto, Urdu, Hindi... and many more) and the 2) Persian outside Iran, eg Dari and Tajik.

It also seems it has nothing to do with Arabic-origin words specifically, as it happens in Persian words too, eg emruz in standard Iranian Persian and Dari vs imruz in Tajik and Urdu).

Here is a better explanation:

Vowel notation is simple but its history is complicated. Classical Arabic has a vowel length distinction; in writing, long vowels are normally written ambiguously by letters known as matres lectionis while short ones are normally omitted entirely (although certain diacritics are added to indicate them in special circumstances, notably in the Quran). Middle Persian also had vowel length, and noted ā with alif ا, ē and ī with yāʾ ی, and ō and ū with wāw و. Short vowels (a, e, i, o and u) were normally not written.

The length distinction of Middle Persian no longer exists in modern Persian. The results of its collapse vary between Western Persian, Dari, and Tajiki, with eight- or six-vowel inventories. However, the alphabet retains the original spellings of most words so that فارسي Fārsī "Persian" is pronounced in the Tehrani dialect fɒrsi and شير shēr "lion" and شیر shīr "milk" is ʃir, while in Dari, these same words appear as Persian pronunciation: [fɒrsi] but ʃer "lion", ʃir "milk".

I assume the shift is to preserve a contrast given that collapse, but you will need to ask someone who really knows Persian to find a minimal pair.

For reference, there is more variation in the pronunciation of Arabic words within Arabic dialects than variation in the pronunciation of Arabic words used across all of these other unrelated languages.