There is a reason for that: if you only change LDL-C without changing HDL-C and Total-C, the Total-C to HDL-C ratio remains unchanged, and that ratio carries a heavier predictive weight than LDL-C alone. The reason why HDL-C plus LDL-C is smaller than total-C is because non-HDL-C comes in different fractions (e.g. chylomicrons, vLDL-C ). You'll see a change in risk if you also change (increase) HDL-C and/or lower total-C.