[xsl stylesheets] reducing font size in formalparas?

Hello,

I am using DocBook XML/XSL to write my biology thesis, and I use
formalparas in caprtions for the figure legends. To make them clearly
distiguishable from the text, I have set their font to sans-serif,
however it looks bigger than the original one.

I failed to modify my customisation layer to reduce the size. Could
any of you give me a hint?

<xsl:param name="toto">
  <xsl:value-of select="$body.font.master * 0.8"/>
  <xsl:text>pt</xsl:text>
</xsl:param>

<!-- toto is the french foo -->

<xsl:template match="formalpara/para">
  <fo:block font-family="sans-serif" font-size="$toto">
    <xsl:apply-templates/>
  </fo:block>
</xsl:template>

<!-- changes the font family but not its size :(( -->

Thank you very much,

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