When exporting a large document in PDF/X-4 2008 for example, and the compression is set to 100 ppi, the image gets exported at 10 dpi instead, and has to be set at 1,000 ppi for the pdf actually read as 100 ppi. ( this happens with any number not just 100 dpi)

This whoever doesn't happen when exporting as Tiff, just when saving as .PDF

I have attached 2 set of screenshots when exporting at 100 dpi and 1,000 dpi and getting the results I was explaining.