Power is always from the back but the difference is the direction. By leading with the finger the difference is the intention. You create a stretch in the hand and forearm which removes space. Every part of the body can move once the part in front of it is stretched. In the case of the arm you can move from the elbow once the hand and forearm has no more space. Once the elbow has no more space you can move the shoulder etc. Every thing becomes full or solid. You want to be as solid as possible while making the opponent as bouncy as possible.