Double Discrete-Time Integrator

Hi. I'm following an example in this link below:

http://www.mathworks.com/products/mpc/code-examples.html?file=/products/demos/shipping/mpc/mpcdoubleint.html

Then, I have changed both integrators into discrete-time integrators. All the configuration parameters are already changed into fixed step. I also redesign the MPC toolbox since the plant is already different. However, I obtained different result. Is there any additional step that I need follow? Thank you.