If you don't like the idea of playing with dl/r and ml/r and are heading towards a variant of narrow diamond, I suggest 5-2-1-2 hard defending. Then the 3DC can help fullbacks. with the oppo's wingers and ml/r. Of course back arrows on fullbacks are mandatory. But my impression is that it won't work, my second team is using 4-1-2-1-2 in all matches and almost always loses to formations with 3 players on each side.