Body can't be identified if people lean against a wall


I want to track body who leans against a wall. And I tested the sample RotatedBodyViewer.

I found it can’t track my body if I stand too close to the wall. (camera is 2m away from the wall)
I also noticed if I stand away from the wall first, let the camera track my body first, then step back to the wall, then my body can also be tracked. but if I lean against the wall at the begin, then it will fails.

is there anything I can do to make it works.