Vertical alignment of text in header

["Andreas Lalloo" <andreas.lalloo@appmind.com>]

Hello!
 
I have a customization layer which for FO output (to PDF via XEP) gives
a header on each page with the default text (chapter title) on a
coloured background. 
 
  <xsl:param name="header.rule" select="0"></xsl:param>

  <xsl:attribute-set name="header.content.properties">
    <xsl:attribute name="background-color">#fdb913</xsl:attribute>
    <xsl:attribute name="color">#ffffff</xsl:attribute>
  </xsl:attribute-set>
 
A similar footer looks nice, but the text in the header has a vertical
position making it almost touch the top, leaving too much space under
it. I would like it to be centered, or possibly with more space above
than below. How would I go about to do that? 

I tried to increase the total size of the coloured header area by
increasing region.before.extent (as described in
http://www.sagehill.net/docbookxsl/PrintHeaders.html) but that parameter
does not seem to have any effect whatsoever. XSL 1.68.1 used. 

  /Andreas