Equation for medical project

We are doing research about choclear implant. We usually insert electrode in the choclea. In order to estimate the right legnth of the electrode, we usually calculate the choclea legnth and make the electrode with the same legnth. However, in some cases the electrode is not reaching to the end of the choclea and that decrese the coverage of the electrode. As a result, the outcome is not optimum. We have a theory about that and we need an enginer or someone with expert in calculation to help is in calculating and mesuring some of the factors that we think might affect the electrode coverage.