Assalaamu alaykum. How far should one go in trying to get the pronunciation right when reciting the Faatihah and Athkaar (pl. of Thikr [expressions of remembrance of Allah]) in prayer, especially in the silent ones? Trying to correctly pronounce each letter results in me opening my mouth widely in order to recite letters like ع and ح silently. It is much easier for me in the audible prayers compared to the silent ones. What is the wisdom behind this? May Allah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

The secret in this is the Waswaas (obsessive whispers) that you are affected with, and you have to ignore and repel it and not pay any attention to it.

You should recite normally, and it is enough that you can hear yourself.

Some scholars do not condition that you hear yourself, but they only require that every letter is pronounced from its Makhraj (point of articulation). Please, refer to fatwa 292798. This does not require opening the mouth wide as you mentioned. Rather, you recite normally and naturally, like all other people, and do not pay attention to such Waswaas.

Allah knows best.