Why does BI Publisher not change the Word header size when changed in the RTF document

Working in PeopleSoft 9.2, Word Pro Plus 2016, modifying the delivered Canada Customs Invoice RTF, which has the same problem BTW,  I cannot get the header to be smaller so that the entire document fits onto one page. I have physically made it smaller using the word ruler on the side as suggested in several Word posts, but nothing changes when rendered in BIP.

Any ideas if there is something hidden that I cannot over rule? Can anyone find a way to fit this entire document on the page?  It looks like there should be plenty of room, except maybe if you have a lot of detail lines. Also, when it does overflow the page, it does not break in a good place. It just breaks in the middle of a table and looks very bad.