Do I have to consider the thickness of the rigid bodies?

*CONTACT_FORMING_xxxxx should be used for stamping analysis. This contact treatment does not consider the thickness of the rigid body. This is generally the desired method because the CAD data for dies are the outer surface. However, the user may specify a proper value for the parameter MST (the third card) in this contact if the die surface is incorrectly described.

Sometimes, people just copy the mesh from the punch to the die and they did not offset the geometry physically. Then a negative value of MST can be used to allow LSDYNA to offset this gap internally.