How High Should the Sutrah Be?
Question

I have read the fatwas on your website regarding the Sutrah and I am still confused about the following two items:
a. In terms of height or width, what is the minimum that will be accepted as a Sutrah?
b. What is the closest and farthest distance can one stand from the Sutrah when praying?
Praise be to Allah.Is having a Sutrah obligatory?
It is recommended for the Imam and the one who is praying alone to pray facing a Sutrah, because of the report narrated by Abu Dawud (598) from Abu Sa`id Al-Khudri (may Allah be pleased with him) who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “When one of you prays, let him pray facing a Sutrah and let him draw close to it.” Shaykh Al-Albani (may Allah have mercy on him) said: “Its Isnad (chain of narrators) is authentic.” 
Purpose of placing a Sutrah in prayer
It says in Al-Mawsu`ah Al-Fiqhiyyah (24/177): 
“It is Sunnah for the worshipper, if he is praying alone or as an Imam, to place a Sutrah in front of him to prevent people from walking in front of him , and to enable him to focus properly on the actions of the prayer. That is because of the report narrated by Abu Sa`id Al-Khudri (may Allah be pleased with him), that the Prophet (blessings and peace of Allah be upon him) said: ‘When one of you prays, let him pray facing a Sutrah and let him draw close to it and not let anyone pass in front of him .’ And because he (blessings and peace of Allah be upon him) said: ‘Let one of you face a Sutrah when praying, even if it is an arrow.’ 
As for the one who is praying behind an Imam, it is not recommended for him to use a Sutrah according to scholarly consensus, because the Sutrah of the Imam is the Sutrah of the one who is praying behind him, or because the Imam is a Sutrah for him.”
How high should the Sutrah be?
The Sunnah is for the worshipper to use something standing as a Sutrah, and it is better if it is the height of the back of a saddle or more, because of the report narrated by Muslim (771) from `Aishah (may Allah be pleased with her) who said: The Messenger of Allah (blessings and peace of Allah be upon him) was asked about the Sutrah for one who is praying and he said: “Like the back of a saddle.” 
An-Nawawi (may Allah have mercy on him) said: 
“This Hadith indicates that it is recommended to place a Sutrah in front of the one who is praying, and it explains that the minimum Sutrah is the back of a saddle, which is the length of the forearm, or approximately two thirds of a cubit. This purpose may be served by anything that he sets up in front of him." (Sharh Muslim, 4/216)
Ibn Qudamah (may Allah have mercy on him) said: 
“With regard to whether it should be thick or thin, there is no definition that we are aware of. It may be thin like an arrow or a spear, or it may be thick like a wall. The Prophet (blessings and peace of Allah be upon him) used to use a short spear as a Sutrah . 
Abu Sa`id (may Allah be pleased with him) said: We used to use an arrow or a rock as a Sutrah for prayer. It was also narrated from Saburah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: ‘Use a Sutrah for prayer even if it is an arrow.’ (Narrated by Al-Athram)
Al-Awza `i (may Allah have mercy on him) said: ‘An arrow or a whip is sufficient.’ Ahmad (may Allah have mercy on him) said: ‘I prefer it to be broader than that, because the words ‘even if it is an arrow’ indicate that something else is more appropriate than it’” (Al-Mughni, 2/38) 
Shaykh Ibn `Uthaymin (may Allah have mercy on him) was asked about the size of the Sutrah for one who is praying. 
He replied: 
“The best Sutrah that a person puts when he prays is the height of the back of a saddle, approximately two-thirds of a cubit, but if it is less than that, it does not matter; even if it is an arrow or a stick, it is acceptable." (Majmu` Fatawa Ibn `Uthaymin, 13/326) 
Standing close to the Sutrah 
The Sunnah is for the worshipper to stand close to his Sutrah, so that he can stop anyone who tries to walk in front of him , because of the report narrated by Abu Dawud (695) from Sahl ibn Abu Hathmah (may Allah be pleased with him) from the Prophet (blessings and peace of Allah be upon him) who said: “When one of you prays facing a Sutrah, let him draw close to it lest satan interrupt his prayer.” (Classed as sound by Ibn `Abd Al-Barr in At-Tamhid (4/195); classed as authentic by An-Nawawi in Al-Majmu` (4/195) and by Al-Albani in Sahih Abu Dawud)
The scholars (may Allah have mercy on them) differed concerning the distance and from where it should be measured. 

Some of them said that the distance is three cubits from the feet of the one who is praying, because the Prophet (blessings and peace of Allah be upon him) prayed in the Ka`bah with three cubits between him and the wall. (Narrated by Al-Bukhari, 506). This is the view of the Hanafis, Shafa`is and Hanbalis, and it is what is understood from the words of Malik, because the distance between the one who is praying and the Sutrah should be as much as he needs to stand, bow and prostrate.  (See: Al-Mawsu`ah Al-Fiqhiyyah, 24/184)
Others were of the view that the distance should be sufficient to allow a sheep to pass, from the place where the worshipper prostrates, because of the report narrated by Al-Bukhari (474) and Muslim (508) from Sahl ibn Sa`d (may Allah be pleased with him) who said: Between the place where the Messenger of Allah (blessings and peace of Allah be upon him) prayed and the wall there was a space where a sheep could pass. 

An-Nawawi (may Allah have mercy on him) said: 
“In the Hadith, Between the place where the Messenger of Allah (blessings and peace of Allah be upon him) prayed and the wall there was a space where a sheep could pass, what is meant by ‘the place where he prayed’ is the place where he prostrated. This indicates that the Sunnah is for the one who is praying to be close to his Sutrah.” 

Some scholars reconcile between the Hadith of Ibn `Umar and that of Sahl ibn Sa`d (may Allah be pleased with them both) by interpreting the Hadith of Ibn `Umar, which mentions three cubits, as applying when the worshipper is standing, and the Hadith of Sahl, which mentions a space where a sheep could pass, as applying when the worshipper is prostrating.” 

And Allah knows best.