I think of modulation as the ability to finely control the brake's power at the lever. Suntour SE brakes are very on/off because the body of the canti is mounted on a spiral and moves forward as the brake is applied. The rotation of the wheel pulls the brake on harder causing a big peak in the braking force at the block/ rim interface. Immensely powerful but impossible to control. Great on tandems, very prone to skidding on solo bikes.