The 'S' duct for the #2 eng in the L1011 would be 'chocking' off some airflow to the engine in the L1011 resulting in less efficient thrust, a disadvantage when compared to the straight thru airflow in the '10.
A careful review of the design will reveal that not to not be the case.
...as the 10-30 was packing 53 tons more than the L1011
Note I specified equal enroute weights, not some 53 tons heavier.