This exercise has two different stages to it. In the first stage the defenders can not leave the square they are assigned to play in within the larger rectangle that they defend. Each defender is in one square. The attackers can move anywhere along their side lines from one square to the next. In the first stage because the defenders can not move out of their square it is not really possible to split the defense from end to end or the long way in the rectangle. Because of the restriction for the defenders to stay in their own square pressure/cover occurs rather naturally. It is possible for the attackers to split the defenders across the short width of the rectangle in the middle.
The second stage of the 4 v 2 Double Square exercise will allow the attackers to split the defense from one end of the rectangle to the other.