How to modify bibliography spacing in biblio.xsl?

Hi,

in the docbook file biblio.xsl a spacing definition is made (about line 87):

[..]
    <xsl:otherwise>
      <fo:block id="{$id}"
                space-before.minimum="1em"
                space-before.optimum="1.5em"
                space-before.maximum="2em">
        <xsl:call-template name="bibliography.titlepage"/>
      </fo:block>
      <xsl:apply-templates/>
[..]

I have some difficulty trying to change these values. If I just copy the
biblio.xsl file, change the values to the desired value and import it
in my customisation, it has no effect. If I include it, the bibliographical
numbering doesn't work any more. I am certainly doing something stupid here,
but I have already been trying to work it out for a while, so a little help
would be very welcome.

(From what I gathered there seems to be no attribute-set to redefine these
values easily, right?)

Thanks in advance,
  Marc Baaden

-- 
 Dr. Marc Baaden  - Institut de Biologie Physico-Chimique, Paris
 mailto:      -      http://www.baaden.ibpc.fr
 FAX: +33 15841 5026  -  Tel: +33 15841 5176  ou  +33 609 843217