The accurate reconstruction of the energy deposition of finite-divergence wide energy spectrum ion beams in multi-material stack detectors calls for substantial computing resources. A transmission matrix model has been developed that uses statistical information extracted from a series of Monte Carlo simulations to build a fast, accurate and flexible algorithm for computing the energy loss of ions in complex heterogeneous detectors. In particular, the ion range and the broadening of the Bragg peak with increasing ion energy were correctly reproduced by the model.