As referenced [here][1], the earliest source I've found for wearing one's tallit with two corners/tzitziyot in front and two back is Ba'al HaItur (c. mid-1100s). But, I'm left wondering where Ba'al HaItur brought this concept from — a concept that later posqim codified (e.g. Shulhhan Arukh, see above link).

In short, upon which source or tradition did Ba'al HaItur found his statement that one should wear one's tallit with two corners/tzitziyot in front and two in back?

  [1]: http://judaism.stackexchange.com/questions/40569/may-one-wear-a-tallit-gadol-with-all-four-corners-in-front#comment107632_40569