Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANE
MDATA_SCULPTBRUSH_SETTINGS_FIXEDPLANEParameter: 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