Pinball radius is measured from the nodes so if the nodes are 2.1 mm away from the solid body, you need a pinball radius larger than 2.1 mm, such as 2.5 mm.
A sheet body has two faces, the TOP and BOTTOM. For Frictional contact, you want the colored face (red or blue) facing the other face in the contact pair.
The colored face (red or blue) is the direction in which it is searching for the other face pair. So you choose TOP or BOTTOM as needed to get the colored face pointing toward the other face.
That is why, for this particular case, choosing TOP makes the red face point in the right direction and setting the Pinball Radius to 2.5 results in a Near Open, while choosing BOTTOM results in Far Open because the red face is looking in the wrong direction.