OK, That worked. I measure a short axis of about 180 millimeters, and a long axis about 189 millimeters. (I may have scaled the picture wrong... so I'm open to corrections here or anywhere in my calculations)

Assuming a 16 tooh cog has a radius of about 32 mm, and a chain stay length of 405 mm (from a Kilo TT schematic at bikesdirect.com), the length of chain between the top of the cog and the top of the chain ring varies from about 411.7mm to about 412.5 mm or, about 0.8 millimeter.

I think I could live with that.