Sitting back and down in Zhan Zhuang (relaxing the lower back, rolling the femur heads forward) allows the kua to close. And, how much my kua can close is an indication of how relaxed and open my lower back is. I'm beginning to get a kinesthetic feeling of extending through my legs to the ground. A Wujifa exercise or method that helps me notice and develop this feeling is Knees Forward, Sit Back and Down. The following describes a typical classroom experience.
Sitting back and down into my heels, I would feel that I was losing my balance and falling backward. To 'maintain balance', I would tense up instead of relaxing further. So to aid in relaxing, I'd be guided to slide the knees forward (shift weight forward) so my weight would be in the center of my foot. However, when I shifted forward I also tended to lean back and my kua would pop out. This prompted another round of sit back and down to close the kua and then slide the knees forward to relax-balance.
This cycle resulted in my routinely "ratcheting down" which ended with me sitting on the floor in a sweaty, confused, frustrated heap. See the following animation. Notice how the entire torso shifts forward with "knees forward" and how the knees stay in place with "sit back and down" practice.
In this animation, I say this "ratcheting down" is the wrong way which may infer that the way I am practicing now is the right way. More to the truth, where I was and where I am now are steps or stages or refinements in my practice.
In recent months, the knees forward, sit back and down has bubbled up as a theme in my practice. However, this time, I'm not getting stuck so much in the earlier "ratcheting down" loop. I now have a better feel-understanding for the singular feeling which I earlier mis-interpreted as a two-step process.
This time around I feel an extending or a lengthening feeling in the quads which has resulted in feeling more weight loading in my thighs and feeling down my calves to the ground.
In the following diagram, "Feeling "A" - Holding" is how, in retrospect, I would describe the feeling that resulted in my "ratchet stance" as in the above animation. I did not know there was another feeling at that time. "Feeling "B" - Letting Go" is the feeling I feel now. After feeling this, I can go back and recreate Feeling "A". The yellow arrows represent the kinesthetic feeling. The red arrows indicate the intention-to feeling. There is both a physical and intention-to activity here. The result is a tactile, observable feeling. (I'm letting go just enough to feel something else than nothing. I'm still holding a lot.)
Of course, "Feeling B" is not the goal, but another first step; another level of refinement. The Knees Forward, Sit Back and Down method helped me to find this feeling in my legs. Because "Feeling A" still dominates, I consciously practice getting "Feeling B" in my stance practice. Remember, "Once you get the feeling, get rid of the method." I still set up my knees and back as in the method but closer together like one move than two and I get to that feeling much more quickly.