detect a table header rupture

Hello everyone,
 
I need to have a < gap > between the header and the first row of a
table.
 
This code works:
 
      <xsl:template match="tbody/row">
   
      <fo:table-row keep-together="always"
keep-with-next.within-column="4" keep-with-previous.within-column="4">
  <!-- add some margin -->
    <xsl:if test="position() = 2 ">
               <xsl:attribute name="height">+15pt</xsl:attribute>
</xsl:if>
         <xsl:if test="@rowsep = '0' ">
            <xsl:attribute
name="border-bottom-style">none</xsl:attribute>
         </xsl:if>
         <xsl:apply-templates/>
      </fo:table-row>
   </xsl:template>
 
 
But, as the table split on another page, the position() test is not
valid, and the gap is missing
 
Any clue?
 
Christian