Dought & clear, - It is makrooh to pray facing a person’s face.

Can I pray if there is someone sitting in a chair in front of me and I
can only see his back?.
Praise be to Allaah.
There is nothing wrong with praying behind someone who is sitting if
he gives you his back; rather it is makrooh to pray facing his face,
if that will distract the one who is praying.
Ibn Qudaamah (may Allah have mercy on him) said inal-Mughni(2/40):
It is makrooh to pray facing a person's face, because 'Umar
disciplined people for doing so. According to the hadeeth of
'Aa'ishah, the Prophet (blessings and peace of Allah be upon him) used
to pray level with the middle of the bed whilst I was lying down
between him and the qiblah. When I needed something, I would not want
to get up facing him, so I would slip away. Agreed upon. End quote.
Al-Nawawi (may Allah have mercy on him) said inal-Majmoo'(3/230): It
is makrooh to pray with a man or woman in front of you, facing him
where you can see him. This was regarded as makrooh by 'Umar ibn
al-Khattaab and 'Uthmaan ibn 'Affaan (may Allah be pleased with them).
And because it usually distracts one. It is also makrooh to look at
what will distract one, such as a garment with decorations on it, or
looking up towards the sky, and other things that are mentioned in the
saheeh hadeeths. Al-Bukhaari said in hisSaheeh: 'Uthmaan (may Allah be
pleased with him) regarded it as nakrooh to face a man when praying.
Al-Bukhaari said: Rather that applies if one will be distracted by
that, but if he will not be distracted, Zayd ibn Thaabit said: I do
not mind; a man does not interrupt the prayer of another man.
End quote.
With regard to one who is sitting with his back towards the one who is
praying, if he does not move and distract the one who is praying,
there is nothing wrong with praying behind him, just as there is
nothing wrong with praying facing one who is sleeping, because of the
report narrated by al-Bukhaari (382) and Muslim (512) from 'Aa'ishah,
the wife of the Prophet (blessings and peace of Allah be upon him),
who said: I used to sleep in front of the Messenger of Allah
(blessings and peace of Allah be upon him), with my legs in the
direction of his qiblah. When he prostrated he would poke me and I
would draw my legs up, and when he stood up I would stretch them out.
She said: There were no lamps in the houses at that time.
And Allah knows best.