Inch power shouldn't be thought of as a technique. It happens every time you punch. When you make contact with your opponent, your arm is still bent. Then when you drive through him, THAT'S inch power. When you develop this ability, then even when your fist is a very short distance, you should still be able to generate a lot of power. That's why I don't think of it as a technique. Rather I think it's part of everything you do in Wing Chun. Every time your fist moves, the inch power is starting automatically.