Hi Hilde,
I am glad to hear that you are finding the course very helpful. I work with Bill Ryan at his school, Toward Harmony Tai Chi & Qigong. I ran your questions by him, and I’ll relay here what he said.
At this stage in your practice, in looking for the physical impetus for the pierce you should focus on the areas of your shoulder blade and armpit. You are right that eventually, the pierce will be initiated in the kwa, as will the foot flicks. So you are on the right track. The general principle here is that “the big moves the small.” So the larger parts of your body will initiate the movements that are expressed in the smaller parts. However, in the beginning it is better to firmly establish that relationship between you shoulder and your arm and hand, before moving further upstream to your kwa.
Dan Winter