Left handed back player.........FREAK!
Only kidding. When your team walks the field, you should look at the back players spots they will be taking off the break. On some fields you may not be able to shoot down the tape at you opposite, because of a blocking bunker, usually on the 50. The options here are wether they will still have an impact on the game from this bunnker, or should they break to another with a better view of the field.
Remember, there is no fixed rule that states back players have to be on the back most line of bunkers, or have to break to their respective corners. Some fields you won't be able to shoot down the line, and will be spending most of your time firing crossed up with your other back man. Decide when walking the field whether you are going to mainly shoot down the tape, or cross field, and then work out positions from there.
One thing I would say is that all your players should be able to shoot with both hands. It is extremely important and will make you a much tighter player, period. Developing this skill will make your player more versitile as well. Imgine that your back left gets shot out, and they were mainly firing down the tape. Your back centre player moves across to take up their position, and cannot shoot left handed properly, if at all. They will not be as effective in the game as the player that could shoot left handed due to a lack of accuracy, and not being comfortable firing.
In summary, walk the fields and decide wether you are able to shoot down the tape, or cross field and they allocate positions from there. The team is flexible and can change sides/positions due to the field design. Make sure that you play players in positions that will maximise their playing ability, not just in positions they 'like' or have played for a while.