My airline seem to operate a standard cost index of 90 on my fleet with occasional variations for operational requirements. That said, we enter CI 0 until top of climb then have a look at the arrival time before adjusting the CI. Generally we have free reign to adjust the CI to achieve an on time arrival or for other tactical reasons (such as getting a better level over Africa). People have also been known to increase the CI after disruption to save the company the cost of another ridiculous overtime payment to the cabin crew.