Controlling Auto Relief

SW 2015.  I'm having some trouble understanding and controlling Auto Relief.  Have a look at the attached file.  You'll see that I've specified an Obround relief with a width-to-thickness ratio of 2.  The thickness is specified as 0.090, so I would expect the relief to be 0.180 wide.  In fact, however, it's much larger then this.  Looking at the flattened part, you'll see that the relief is a square with rounded corners.  The relief ratio seems to control only the radii of these corners - the straight sections connecting them remain the same length.  What's driving the length of these straight sections?

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