Since my previous post, I went of vacation for 2 weeks during which time I took a break from training. This was a conscious decision on my part - partly to give my body some time off and partly to give my mind the chance to mull things over in my unconscious for a while. Seems to have worked because, once I returned, it felt like there was a spotlight on a number of sticking points in my practice.
One sticking point was the issue I discussed in my previous post, where I described how to do a weighted pivot (on the left foot) by closing the (left) hip - this allows you to pivot without having to shift your weight back first.
While practicing this movement, I noticed I was still shifting my weight back slightly, although much less than previously and that my balance still felt a bit off. I finally realized that I've been pivoting on the extreme back edge of my heel. Based on my experiences with push-hands/spinning-hands, once your weight is in the back of the heel, you can be
pushed right over - if you're weight does move to your heel, it can't move past the center of the heel and I realized this applied to the pivot as well.
I've adjusted my pivots now by moving the pivot point to the center of the heel and it has made things a lot easier. As a bonus, I find that I am also able to move my foot further along the arc of the pivot before torquing my knee, which gives me better mobility.