HH says the movement challenges shown in the video are not related to stance width. Slant board training is about learning to balance on the edges and we can't do that if we are using the wrong movements or leaning on the poles in place of balancing on the edges.
See this thread for a good discussion on the value of learning to balance on edges with the slant board:
viewtopic.php?f=1&t=4030
Then revisit the instruction and movement shown in the videos located here:
https://harbskisystems.com/pages/slantboard-training