I was reading a review of the popular Samyang Fisheye lens, and it started talking about the NPP locations, and provided this image showing different NPPs for different 360 pano intervals- a different NPP for 60, 45, and 90.

Everything else I've read talks about each lens having a single NPP- and by the very nature, why would the NPP change if the interval angle changes?

Just looking for some enlightenment, thanks.