Related to this topic is the opening and closing of the body to generate power. This can be easily studied through the Lit Chui which is similar to Tai Chi’s Part the Wild Horse Mane technique.
When you first learn the technique use big, expansive movements as this allows you to feel your body better. This involves using the upper body as well to open and close.
But once you get the hang of it reduce the movements to as compact as you can without losing the speed and power. Eventually you will feel as if you are using the dantian to whip the power out.
If you use this power in the first movement of Ip Man’s Wing Chun Siu Nim Tao third section it will add to your power without slowing you down. All it takes is understanding what you are doing and practice the hell out of it.