Getting incorrect output from a discretized linear parameter varying state space model.

I identified the parameters of a SISO linear parameter varying simulink model by NLSE tool-box of MATLAB R2013a. One of the model parameter is a function of the previous model output, which has been represented by using a unit delay/memory block in the simulink model.

Now I'm trying to get the output from the state space model of the same system by using the model parameter identified in earlier step. I order to get output, I used 'c2d' command at Ts=2s for discretizing the continuous state space model, however, the output is not matching with the output of the simulink model. According to my best knowledge, as the model parameters are same the output should be same for the simulink and state space model but the state space model output is underdamped in compasision of the simulink model output. Then I changed Ts=1.8s (by trial & error) then it is giving quite accurate result however the sample time in both the simulation and experimental data, based on which parameter estimation has been done, were 2 sec., that's why I set Ts=2s.

My question is, why for Ts=2s the discrete state space model is not giving accurate result?