sculpt/description/toolsculptbrushflatten.hParameters are accessed with cinema::C4DAtom::GetParameter() and cinema::C4DAtom::SetParameter(). See Parameters.
Parameter: MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE
MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANEMDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_OFFMDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_MOUSEDOWNMDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_WORKPLANEMDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_CUSTOMParameter: MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_CUSTOM_HIDEONSTROKE
MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_CUSTOM_HIDEONSTROKEParameter: MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_CUSTOM_SIZE
MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_CUSTOM_SIZEParameter: MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_DEPTH
MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE_DEPTHParameter: Smooth
MDATA_SCULPTBRUSH_FLATTEN_SMOOTH