No time for proper testing, but at least in Sigil this seems to work (even with only height set at 60% and width left at 100%:
Code:
<div>
<svg xmlns="http://www.w3.org/2000/svg" height="60%" preserveAspectRatio="xMidYMid meet" version="1.1" viewBox="0 0 930 1314" width="60%" xmlns:xlink="http://www.w3.org/1999/xlink">
<image width="930" height="1314" xlink:href="../Images/filename.jpg"></image>
</svg>
</div>