:wa:
Hope this helps:
It is recommended, after completing the obligatory prayer with the imam, for one to move to a different spot to pray one’s voluntary (sunnah) prayers in order to break the rows.
Additionally, it is particularly recommended for the imam, himself, and disliked for him not to do so, in order that any latecomer can plainly see that the obligatory prayer is over.
[Shurunbulali, Maraqi al-Falah; Kasani, Badai` al-Sanai`]
Furthermore, there are a number of narrations (hadiths) on this very issue. From amongst them is that which is narrated from the Messenger of Allah (Allah bless him and give him peace) that he said, “Let not the imam pray in the same spot in which he prayed his obligatory prayer until he moves away from it [i.e. that spot]” [Ibn Majah]
And Allah knows best.
Wassalam,
Tabraze Azam
http://seekershub.org/ans-blog/2011/11/30/is-there-any-basis-for-moving-to-a-different-spot-to-pray-sunna-prayers/