The key to creating inset doors is the OVERLAY (OL) field.
When set to a positive value the resulting door has a rim all around of the exact width specified in the OL field. A value of 0 produces a door that is the exact size of the opening.
A negative OL value produces a door smaller than the opening; an INSET door. The gap between the door and the frame is the exact value specified in the OVERLAY (OL) field.