If you are using Sigil or other software that generates an automatic table of contents, you could also add a Heading tag to the file that has your cover image. You can style the header to "display: none" so it doesn't interfere with the placement or aspect ratio of the image.
This has worked for me, using Sigil to create the ToC. Display is fine in ADE, v 1.8.
Code:
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>cover</title>
<style type="text/css">
/*<![CDATA[*/
body {margin:0; padding: 0; border-width: 0; }
@page {margin: 0; padding: 0; border-width: 0; }
h1 {display: none}
div {
text-indent: 0em;
text-align: center;
}
/*]]>*/
</style>
</head>
<body>
<div>
<h1 id="heading_id_2" title="Cover"></h1>
<svg xmlns="http://www.w3.org/2000/svg" height="99%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 600 800" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="800" width="600" xlink:href="../Images/cover.jpg"></image>
</svg>
</div>
</body>
</html>