PDFPage setBounds behaviour on cropBox differs on iPhone and iPad

I am trying to crop a pdf to remove 100 points from the top and bottom of the page. The mediaBounds of my pdf is size 612x792 and the origin is 0,0. My code the set the bounds of the cropBox is:

page.setBounds(CGRect(origin: CGPointMake(0,100), size: CGSize(width: 612, height: 592)), for: .cropBox)

This sets the origin at 0,100 and the cropBox size to be 200 less than the mediaBox size. This works on iPhone, but on iPad I need to set the height to be 692, otherwise too much is cropped. Is this a bug or is there an explanation?

PDFPage setBounds behaviour on cropBox differs on iPhone and iPad
 
 
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