Thanx a lot.Wa salam,
Look up Jazriyah lines 20-26 on sifaat. 10 sifaat are mentioned in these lines. Also it is mentioned in kitaab Al-Nashr fil Qir'at al-Ashr by Allamah Jazry as well as in al-Hirz ul Amani wa Wajh ut tahaani (more commonly known as Shatibyaah) by Allamah Shatiby.
Ist`ila literally means to seek elevation. Technically it means the elevation of the tongue
toward the palate while pronouncing the letters of ist`ila. خ ص ض غ ط ق ظ
Out of these letters of Ist`ila , ص ض ط ظ are also letters of Itbaq. Itbaq literally means to encompass, cover, close, adhere. Technically it refers to the
center of the tongue adhering to the central palate when the letters containing itbaq are pronounced.
Istifal literally means to remain low. Technically it means that the tongue is not elevated
toward the palate while reciting these letters. All letters besides the letters of isti`la are
the letters of istifal.ء ن ش ر ح د ي ث ع ل م ك س و ف ت ج ه ز ب ذ ا
In order to keep elevation of letters of Ist`ila, mouth is vertically opened to give it full mouth/tafkheem.
Where as rest of the letters of Istifal tongue is not elevated so naturally mouth is not vertically opened - rather lateral to keep tongue not from elevating. So they are empty mouth giving tarqeeq.
There is more to it which comes as sifaat lazimah (permanent qualities) and sifaat Aa'ridah (temporary qualities) which requires much more typing so I will leave, and have you study Jazriyaah, if you haven't already done so.
These cant be learned by reading books only or watching youtubes, you must seek a Qaari with Ijaazah to learn from face to face.