RTRamya Thirugnanam Syncfusion Team February 16, 2019 04:22 AM
Header/Footer supports only From Top/From Bottom respectively. Setting Right/Left margin can only set to the entire Page using PageSetup dialog. In order to attain your requirement(header to span all width) You can use other formatting options for position the items.
Form the shared screen shot we are able to see difference in header section. Could you please share the document in which this behavior is faced, so that we can investigate further on this scenario, provide the solution at earliest.