Hubert: Am I right when I say the shins are parallel to the body’s plane in this position ?
Well the body has three major planes so the question in that form lends itself to misinterpretation.
If you are doing this pose either sitting or supine then the shins would be perpendicular to the mid-sagital plane of the body.
Another way to think of it is that the shins are parallel to the front edge of your mat.
The shins are parallel to the frontal plane but perpendicular to the sagital plane.