[sbrthrds]

It depends on the complexity of the model as to whether the kind of thoughts being put forward here are required.

From the original question, since no specification of point of attachement is given, we should assume a simple model, meaning everyone's free body diagrams are "incorrect". In this simple model, the forces in the diagram should be applied at the centre of mass.

The components of each vector P are then equal whether the box is being pushed or pulled, as they are equivalent to Pcos30 in the positive x-direction and Psin30 in the positive y-direction and should be drawn acting at the centre of the box in the diagram.