No perfect circles in space...

[Anomalocaris]

The key seems to be for a static planar circle not moving with respect to the observer, its radius must be 2 X pi X R. But when a real object is given the motion required to place it in what classical physics would describe to be a circular orbit around the sun, the motion of the object puts it in accelerated frame of reference with respect to the sun or any notional static points along its orbit. So an real orbit is not exactly analogous to a static planar circle.