SB seems to over-index on low cost indices.
Some airlines use a fixed CI, which you can obviously set in SB, but many others have a dynamic CI range similar to SBs calculated dynamic cost index, but they have high limit and a low limit to it.
Would you please consider a system that allows users to set a CI floor and ceiling, within which SB is then free to generate an appropriate CI based on conditions?
For example, you could set A320s to have a range of CI 10 to CI 70, and SB will generate a CI within that range that will never be below 10 or above 70.