An inverse SEA procedure that mimics the Experimental SEA (ESEA) is used in order to obtain the Coupling Loss Factor (CLF) of structural junctions. The main differences with respect to ESEA are that: 1) the subsystem energies and input powers are obtained by means of numerical simulations; and 2) the internal damping is imposed and must not be determined a posteriori (which allows reorganisation of the equations). The numerical model is based on the Spectral Finite Element Method (SFEM). This helps in order to cover a large frequency range without increasing the number of elements and to efficiently perform a large number of simulations with different load configurations (both aspects are required by the inverse SEA procedure). The contribution analyses several aspects such as: various options to obtain the input power from the numerical model; possible modifications in the background SEA model in order to avoid negative CLF values;assessment of the validity of the SEA hypotheses; possible shortcuts in order to avoid matrix singularities or to deal with abundant data. Finally, it is shown how the CLF values obtained for simple configurations can be used to model the response of more complex structures.