Look into the use of Alignment tabs for positioning header/footer elements horizontally. These position elements relative to the margins rather than according to tab settings. They work in Word 2007 and later.

Sections / Headers and Footers in Microsoft Word 2007-2013

These are relatively new and are independent of the tabs set in the paragraph format. They are only available in the Header/Footer Ribbon (although they can be used anywhere in a document).