Models in the incomplete rear rank must normally be kept as close to the centre as possible. If the unit is fighting to its flank, the models in the incomplete rank are moved in contact with the enemy and fight normally (See Diagram 36.1).
If the unit is fighting to its rear, some enemy models might end up not in base contact with the enemy because of the models in the incomplete rear rank (Diagram 36.2 shows an extreme case). In this situation, models can attack the models in the enemy unit, even if not physically in base-to-base contact. In reality, the chargers would not have stopped one step away from the enemy and would have moved in, finishing their charge.