Think this has been around before, and below is probably how you solved it.
PDFs in AC are published to the paper size you set them at, say A1, which includes margins, as though it was the piece of paper. So if you then go to print the PDF and say fit to paper, it will only print at 96%, as it is printing the A1 PDF inside your printers default margins. You have to tell the printer you do not want any page scaling for it to be to correct scale.
This works fine in PDF readers if you are printing A1 to A1 or A3 to A3, but if you want to print an A1 at exactly 50% to A3 to maintain scale, you can't with some readers. You can't get 50% reduction in Acrobat Reader for some reason, and so we use Foxit.
Ian C