To specify additional discretization options beyond the discretization method, use c2dOptions. Here, the discretization options set discopts specifies both the Tustin method and the prewarp frequency. The prewarp frequency is 3.0 rad/s, the frequency of the notch in the compensator response.
Using the Tustin method with frequency prewarping yields a better-matching frequency response than Tustin without prewarping.
Compare the frequency-domain response of C and Cdz.