Hi Felix - when you pick the flower it reports the bounding box of the flower, and since the flower does not have any geometry at the extreme positive and negative x axis locations where the circle does, its bounding box is smaller than the circle.

You can see this by selecting the flower and using the BoundingBox command - the yellow box show here are the bounding box of the flower:



Note there how the bounding box around the flower is smaller than the circle.

You were probably thinking more along the lines of a spherical bounding volume, but the one that MoI reports there is an axis aligned bounding box.

- Michael