What happens on the Kobo device? Is the problem the page display while reading, or the generation of the cover images for use in the library? And which one are you testing with?
From what I can see that is OK, assuming the image is in the place the src property points to. The code I use, cribbed from someone around here, is:
Code:
<div>
<svg xmlns="http://www.w3.org/2000/svg" height="100%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 389 640" width="100%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image height="640" width="389" xlink:href="../Images/cover.jpeg"></image>
</svg>
</div>
With the sizes changed to match the image size. That works will on both Kobo devices I have.
I'd be happy to try your file and see what happens. Send me a PM with a location I can get it from or for my email address to send it to.