DLC on the L1011 was primarily required to achieve the necessary consistent accuracy of the Autoland touchdown point for autoland certification
This whilst maintaining an acceptably constant flight deck pitch up angle for low level runway sighting by the pilot at Decision height in conjunction with the correct pilot eye height indicator for autoland decision or man land in event of a late malfunction.
That is what the L1011 test pilots and flight engineers told me, but Hell what do they know?
Heard a rumour the L1011 autoland system was designed by the old Trident autoland team hired enmass and moved to the states.