The Rambam does not mention how to wear a Tallith; and refers to wearing it as עטוף - but I cannot find where he defines that concept. Those communities - like the Teimanim - may be relying on the Rambam without subsequent Poskim/Meforshim.
The Tur and Bet Yosef define עטוף as covering your head, face and body - which is why we wrap our heads in the Tallit before wearing it.
Most other Poskim seem to go like the Shulchan Aruch, as I elaborated here that require one to have 2 in front and 2 behind.
A quick look in the Bet Yosef shows that the source for putting 2 in front and 2 behind is the עיטור as well as the רוקח who brings a Medrash on the Pasuk in אז ישיר that states
והמים להם חומה the water behind them was warned not to harm them as they would be wearing 2 ציצית behind them as well as the knot of their תפילין.
The Bet Yosef also bring the הגהות מיימון at the end of the Rambam's Hil. Tzitzit who quotes a Yerushalmi that a child is not obligated to be taught about ציצית unless he can keep 2 in front and 2 behind.
We do not seem to have this Yerushalmi - and maybe the Rambam did not, either.