The Preview picture in Door/Window Settings uses some Wall settings to provide useful context.
For example:
•For an Empty Opening, the 3D Preview picture also indicates the thickness and surfaces of the surrounding Wall, to provide some context. (In default Door/Window Settings, the default Wall parameters are used for the Preview.)
•When showing Casing, Frame and/or Sill in the 2D/3D Previews, the thickness of the Wall setting is used.