Making The Inside Gum Work

A question in tonights live stream class

After using a Bong, Lap, Fak Sau against a strike, if another strike is thrown, a common follow up to use is the inside Gum and Punch, similar to section 2 of Siu Lim Tau or section 3 of the Wooden Dummy, but how do we make sure this technique is strong enough?

Hopefully this video will give some answers: