We introduce a refined formulation of the Fragmentation Environmental Index (FEI), designed to assess changes in the Low Earth Orbit (LEO) environment resulting from the fragmentation of a specific mass. The index quantifies this impact by comparing overall LEO criticalities before and after the fragmentation event. To highlight the contribution of smaller debris, we enhance the index by incorporating weighting factors tailored to optical and radar surveillance networks. Testing of the upgraded FEI on a series of simulated fragmentation events shows that it can characterize both the perturbation to the LEO environment and its temporal evolution, providing a more accurate quantification of the short- and medium-term impact of debris clouds compared to the original formulation.