The Termi for bikes with the later black swingarm has the flattened section to help with clearance, the earlier grey swingarm bikes didn't need it. If you follow the link below and scroll down the page you'll see a variety of Termi systems and the last one is a 57 mm kit which clearly shows the 'flattened' section.
http://www.ducatisaarland.de/abc.php?typ=14