The Constraint settings can be set to
Nitsche constraints (default),
Pointwise constraints or
Weak constraints. The
Nitsche constraints option ensures continuity of the diffusive flux. This option may work better than the
Pointwise constraints or
Weak constraints when the meshes of the source and destination boundaries do not coincide. Alternatively, select the
Pointwise constraints option. Select
Weak constraints to replace the standard constraints with a weak implementation.
) and select Advanced Physics Options in the Show More Options dialog box. 
) and select 
) and select