This work introduces the resonance index (RI) technique, a new methodology for exploring magnetohydrodynamic induced fast ion (FI) losses in tokamaks, with applications to cases involving toroidicity induced Alfvén eigenmodes and neoclassical tearing modes in ASDEX Upgrade. The RI technique focuses on the impact of the FI phase space topology on the mechanisms that drive FI loses and aims at the interpretation of signals from the FI loss detector (FILD). A fresh approach to orbit labeling is presented, linking the FI phase space with the FILD plane. Key findings, such as notable changes in RI and a distinct maximum along the boundary dividing phase space regions emphasize the importance of phase space topology in resonant interactions. As a deliberately zero-order model, RI retains only the axisymmetric guiding-center motion, assumes the toroidal canonical momentum to be effectively invariant, and folds the unknown mode structure into a single width parameter. These simplifications sacrifice quantitative accuracy for speed and transparency, making RI a qualitative—but rapid—tool for interpreting FILD patterns with surprising success in reproducing experimental findings.