Huang Zhicheng's bagua is Yin Fu via Gong Baotian and you can see the s shape stepping at the 11:18 mark - I learned this very early and did the walking with another person as a figure 8 and when we met in the middle did two person spear hand strikes before completing the opposite
https://www.youtube.com/watch?v=dLUA8JNHr_o
Fan Style Bagua Zhang 8 postures walking in S Shape
https://www.youtube.com/watch?v=MXqi-qf1xQU
Huang zhi cheng bagua
In the video, Master Huang Zhi Cheng demonstrates the Bagua Zhang style jibenggong (base).The master shows in detail the basic technique of the style: movements, the position of the palms, 8 basic palms, the basic ligaments of the style. The training is carried out with repetition and detailed explanation