Space before and after section title

Hello,

I'm trying to modify the space before a section title (about twice of  
the title font size) and after the title (the minimum available).

I used something like that :

	<xsl:attribute-set name="section.title.properties">
		<xsl:attribute name="font-weight">bold</xsl:attribute>
		<xsl:attribute name="space-before.minimum">30pt</xsl:attribute>
		<xsl:attribute name="space-before.optimum">25pt</xsl:attribute>
		<xsl:attribute name="space-before.maximum">20pt</xsl:attribute>
		<xsl:attribute name="space-after.minimum">12pt</xsl:attribute>
		<xsl:attribute name="space-after.optimum">12pt</xsl:attribute>
		<xsl:attribute name="space-after.maximum">12pt</xsl:attribute>
	</xsl:attribute-set>

But the result is not really what I expected. I would like that :


this is the last line of a para.


The title of the next para (which will be 1.2*para font size and bold)
The first line of the next para.

How can I do that ?

Thanks in advance,
Jacques