Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Falloff Matrix
GV_MG_FALLOFF_MATRIXParameter: Sample Position
GV_MG_FALLOFF_POSITIONParameter: Normal Direction
GV_MG_FALLOFF_NORMALParameter: UVW Coordinate
GV_MG_FALLOFF_UVWParameter: Array Size
GV_MG_FALLOFF_ITERATIONCOUNTParameter: Index
GV_MG_FALLOFF_ITERATIONParameter: Value
GV_MG_FALLOFF_VALUEParameter: Color
GV_MG_FALLOFF_COLORParameter: Direction
GV_MG_FALLOFF_DIRECTION