Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Switch To Field
FALLOFF_SWITCHTOFIELD
Parameter: Field
FIELDS
Parameter: Shape
FALLOFF_MODE
Parameter: Invert
FALLOFF_INVERT
Parameter: Visible
FALLOFF_VISIBLE