Parallax on mobile is pretty messy/not user friendly, so it’s deactivated on purpose to increase user experience.
On mobile the background image size should be set to cover, so as much as the image will be shown as possible. Does it not look right?
Page Header/Sections will be going through a user experience overhaul before any more parallax options are added at this point.
Top/Bottom padding simply adds spacing to the top and bottom of the inside content of the section.
More top/bottom padding will make the section taller etc..