The simulation of time-harmonic electromagnetic waves in wide domains (in terms of wavelengths) with classic methods, as Discontinuous Galerkin, induces large linear systems : their direct resolution becomes memory-prohibitive while the matrices are poorly adapted to iterative methods. On the contrary, Trefftz methods embody a framework which is able to deal with such configurations. Yet, the classic choice of plane waves as basis functions limits their efficiency and usefulness in heterogeneous or challenging domains. Thus, a quasi-Trefftz approach can be considered by using a Flux Reconstruction method to design an adaptable and robust Trefftz space.