FO: put text on top of a graphic, FOP versus AH

I have a cover graphic for a PDF that fills the page, and I need to put 
the title text on top of it.

The FO code below works with FOP, and the text is placed on top of the 
graphic. But when I run it with Antenna House, the graphic is placed on 
top of the text, obscuring the text.

How can I get this to work with Antenna House?

Thanks,
Mark
------------
   <fo:page-sequence force-page-count="auto" 
master-reference="front-matter">
     [... static-content header, footer...]
     <fo:flow flow-name="xsl-region-body">
       <fo:block-container absolute-position="fixed" top="-1mm">
         <fo:block>
            <fo:external-graphic content-height="138%"
src="url(file:/C:/path/dita-ot-3.2.1/temp/Customization/OpenTopic/common/artwork/CoverArt.jpg)"
           />
         </fo:block>
       </fo:block-container>
       <fo:block font-family="Lato, Arial, Arial Unicode MS, Helvetica" 
space-before="80mm"
         space-before.conditionality="retain" font-size="28pt" 
font-weight="bold" line-height="140%"
         color="#4E565B" margin-top="63mm" margin-right="60mm">COVER 
TITLE TEXT </fo:block>
     </fo:flow>
   </fo:page-sequence>