controlling ToC depth for an article with nested sections (DB5)

I'm currently stuck in trying to get DocBook to produce ToCs in FO/PDF 
output for nested sections more than 0 levels deep. I see a ToC for 
article/section, but not one for article/section/section.

In my customization layer, I have:

   <xsl:param name="generate.toc">
     appendix toc,title
     article  toc,title
     section  toc
   </xsl:param>

   <xsl:param name="generate.section.toc.level" select="5" />

Using 1.73.0 (NS) and a DB5-valid doc.

Any ideas?

Thanks,

Brett