Question Summary:
Should one not cross the area in front of someone performing Salaah?

Question Detail:

 
I've heard from a shaykh that one should not cross the area in front of someone performing salah (the area specified being 2 saffs.) Does the saff the person performs salah in count as being part of the area that musn't be crossed or does the area extend for 2 saffs beyond the saff the worshipper is situated in?
Also, if, after the jammah concludes its prayer, there's a latecomer behind me who rises to makeup the rakahs he's missed, is it permissible for me to move to another spot before he finishes his prayer? If I have sunnah mukadahs to complete am I allowed to delay them until I can move somewhere else once the person finishes his salah?
Please advise me on the best course of action to take in a situation like this.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Please take note of the following points[1]:
1). In a small masjid, a person may not cross in front of the musallī (one performing salah) except if there is a barrier (There is no question of two rows). A small masjid is less than ~335 meters sq. For example, a masjid which is 18.4 × 18.4 meters is a big masjid.
2). In a big masjid (334 meters sq. or more), a person may cross in front of the musallī from beyond the musallī’s field of vision whilst he is looking at the place of sajdah. Mufti Rashid Ahmad Ludhyanwi rahimahuAllah has said that this is a distance of approximately two rows, including the musallī’s row.
3). You may perform your sunnah salah in the same place you had performed your fard salah. There is no need to move from your place, especially if there are people completing their salah behind you.   
And Allah Ta’āla Knows Best
Hisham Dawood
Student Darul Iftaa
Chicago, USA 
Checked and Approved by,
Mufti Ebrahim Desai.