DynaPDFMBS page size

In code, I create a PDF and set the size:

paperwid_in_points = 1681.511
paperhei_in_points = 1048.818
call pdf.SetPageWidth(paperwid_in_points)
call pdf.SetPageHeight(paperhei_in_points)

The PDF, when examined in Adobe or other tools, shows an incorrect size:

image

By my calculations, with PDF at 72dpi , the sizes should be

1681.511 / 72 * 25.4 = 583.199mm
1048.818 / 72 * 25.4 = 369.999mm

and Google agrees with me:

Where did this extra unwanted 30mm come from?