Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Reference
GV_HAIR_PROXIMITY_OBJECT
Parameter: Mode
GV_HAIR_PROXIMITY_MODE
Parameter: Point
GV_HAIR_PROXIMITY_INPUT_POINT
Parameter: Index
GV_HAIR_PROXIMITY_POINT_INT
Parameter: Guide
GV_HAIR_PROXIMITY_POINT_GUIDE
Parameter: Segment
GV_HAIR_PROXIMITY_POINT_SEGMENT
Parameter: Position
GV_HAIR_PROXIMITY_POINT_VEC
Parameter: Segment Delta
GV_HAIR_PROXIMITY_POINT_T