IC by speed forcing is not best practice because it forces speed and not torque. The S Ramp function is performed in the drive system controller and provides the acceleration signal. The acceleration signal is multiplied by a speed factor in the drive controller and summed with the S Ramp.
The difference in S Ramp minus the drive speed is minimized by adjusting the factor while ramping the speed without web.
IC calibration involves repeated accelerations and deceleration without web. During the speed changes, monitor the difference in speed between the S Ramp and drive speed. The speed difference can be calculated in the drive controller and trended using the drive commissioning software. Adjust the scaling factor to minimize the speed difference.
A number of factors affect the accuracy of setting IC by this method. The most important is the lag introduced by the speed filter in the drive. I suggest temporarily eliminating the filter for this procedure.