A lot depends on how the XML is structured - I use XML Notepad to view the XML. In my examples below, I'm using R43500 (PO Print) where the page header contains static info except for the page number. However, you won't normally use the page number from the XML - you'd let the template take care of page numbering.
So from my POV, I think you are after the static data.
When you map it, the BIP default is to use relative addressing to refer to the XML data field. For example, in a RTF template, the data field placeholder for Company Name would look like <?szCompanyDescription_ALPH_ID17?> if you mapped it using the BIP add-in for Word.
What I do is refer to the values using absolute addressing. This way, no matter which XML grouping (loop) I'm in, I can explicitly refer to the header values - which are in a different level/group. So for Company Name in R43500, the data field placeholder I'd use would be <?/R43500/PageHeaders/Page_Header_S43/szCompanyDescription_ALPH_ID17?>