On Jan. 6, 2015, I have finally completed the long term goal of 10,000 yilus. I started counting on Aug. 4, 2010, and so it took 4 years and 5 months to reach the goal.
Master Chen's comment on the yilu from the video above:
The head is not pulled up enough. If the head is pulled up, the curved back is good, otherwise it is bad. You still need to train to form a central axis.
In this video, Master Chen showed how to have a vertical line when doing yilu: