how to get rid of leading/trailing space in verbatim?

still hammering away on some picky customization.  how can i reduce
the amount of vertical space generated both before and after a
verbatim environment?

  i have a couple <screen> and <programlisting> elements, and i
added the verbatim shade property to emphasize them.  when i did
that, i noticed that there was considerable (shaded) space both
at the top and bottom of the displayed verbatim environment --
that is before the first line and after the last line.

  i went looking for how to reduce this (wasted) space, and
tried:

---------------------------------

<!-- Verbatim properties. -->
<xsl:param name="shade.verbatim" select="1"/>

<xsl:attribute-set name="verbatim.properties">
 <xsl:attribute name="space-before.minimum">0.0em</xsl:attribute>
 <xsl:attribute name="space-before.optimum">0.1em</xsl:attribute>
 <xsl:attribute name="space-before.maximum">0.1em</xsl:attribute>
 <xsl:attribute name="space-after.minimum">0.0em</xsl:attribute>
 <xsl:attribute name="space-after.optimum">0.1em</xsl:attribute>
 <xsl:attribute name="space-after.maximum">0.1em</xsl:attribute>

<!--
 <xsl:attribute name="line-height">160%</xsl:attribute>
-->
</xsl:attribute-set>

-----------------------------------------

  i thought that set of similar attributes would reduce the amount
of "before" and "after" space, but it didn't seem to make any
difference.  am i misreading the function of this attribute set?

  any hints?  

rday