precise location of % scaled symbols

precise location of % scaled symbols

mozilla, opera, safari and amaya each display the attached example  
uniquely.

This arose as I could not find an easy way to accurately place scaled  
symbols using % on a map here:
http://www.peepo.co.uk/temp/moulin/moulin070616.svg

each of these four user agents displaces the symbols uniquely.

regards

Jonathan Chetwynd

variation based on:
http://www.w3.org/TR/SVG11/images/struct/Use01.svg

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<svg xmlns="http://www.w3.org/2000/svg"
      xmlns:xlink="http://www.w3.org/1999/xlink"
 >

<defs>
<symbol id="myRect" viewBox="0 0 200 1000">

<rect width="30" height="50" />

</symbol>

</defs>

<rect x="165" y="180" width="65" height="20" fill="#dddddd"/>

<use xlink:href="#myRect" x="20" y="185" width="30%" height="20%"  
fill="#ff0000"/>

</svg>