Your take on math is roughly what I figured, but I'm not quite sure and I'm also not show how to edit this "value" with the attribute editor. Appreciate the input though.
Looks like the formula used in that post is either outdated of how pen/armor used to work or was modified. As you know penetration of a vehicle is simply penetration/armor to determine its chance to penetrate. So there doesn't seem to be a need to worry about penetration coefficient unless you want to do something with it.