Is it obligatory to protect the face during stoning, and how is the person stoned put to death while protecting their face, and what is the size of the stones used for stoning?

It is mentioned in Sunan Abu Dawud that the stoning of a woman should be with a pebble the size of a chickpea, but this hadith is weak. It is also mentioned in Sunan Abu Dawud and An-Nasa'i a weak hadith that prohibits striking the face during stoning.

The jurists have explicitly stated that the stones should be of medium size, neither so large as to kill instantly, nor so small as to prolong the torture. The stoning should target fatal areas such as the navel and above, while avoiding the face and private parts. The person being stoned will die from injuries to areas other than the face.