The shock valving inside full coilovers is better equipped to deal with the higher spring rate. The shock on full coilovers is always performing at its maximun ability, versus a separate shock which is never performing at its maximum ability because it is compressed due to the lower stance of the car via the springs. The shaft on full coilovers is often larger in diameter than separate shocks, eliminating any flex in the shocks. Full coilovers also have a larger nitrogen capacity, lowering the overall heat of the nitrogen, creating less bubbles, making every piston stroke more efficient. When the piston is inefficient the shock is more easily compressed, making for bad performance.
Ride in a car with nice full coilovers and you will get the picture.
__________________
|