Header of PDF overlapping body

See more:

PDF

I'm generating PDF file with FOP, but my header contents are not fixed, they keep on changing with each report and with each locale of browser.
Because of this my static width / height setting like

margin-top="0.25in"

or

margin-top="0.95in"

is failing for some reports, i.e my header is overlapping with body contents.
Is there a generic solution which can fix this?

[edit]Tidied up a little to clarify question - OriginalGriff[/edit]

More details:
Header of pdf is overlapping on the contents of body of pdf, because of which I am not able to see my top contents in my body of pdf document.
I want to way by which ,if header contents are increased then body should start after the layout of header.
But in pdf api it is required to set:

<fo:region-body  margin-top="1.25in" margin-bottom="0.50in" />
                    <fo:region-before extent="1.25in"/>
                    <fo:region-after extent="0.50in"/>

which is causing problem bec. when my text in header increases beyond 1.25in which is specified in

<fo:region-body  margin-top="1.25in"

then in that case header text overlapps body text.