[en] We report a new method of level-fitting calculations (FS-fit, fine structure fit) in a large multiconfiguration basis. This method allows inclusion of all electrostatic and spin-orbit interactions predicted for the system under study. This has been achieved without accruing interaction parameters faster than level data by relating interaction parameters to the ratios determined on the basis of their effective quantum numbers. The method has been tested for the system consisting of 33 configurations of Si I and a very good FS-fit has been achieved with a mean deviation of 4 cm^-1. The method proposed should also yield eigenvectors that can be used to calculate other physical observables with a comparable precision. Moreover, we are able to predict a destructive interference effect on the line strength due to the relative phases of eigenvectors. An example of the absence of some transitions in the silicon spectrum is discussed. (orig.)