In the analysis of the propagation of electromagnetic waves in the electron cyclotron frequency range, in both isotropic media and magnetoactive plasmas, the role of diffractive effects, which are not accounted for by geometrical optics, may no longer be neglected when highly collimated beams are to be employed. Moreover, when lenses, mirrors, refractive gradients and/or wave cut-offs are placed along the beam trajectory, the very concept of independent optical rays tends to introduce singularities, which do not always correspond to physical features. A quasi-optical approach has previously been shown to present the advantage of allowing a description (at the lowest order of approximation) of the diffractive widening of the beam. The specific aim of this paper is to test, when reflection, refraction or beam focusing indicates the need for particular attention, the solution method employed within such an approach. The results presented here concern the propagation and power deposition profiles, in a number of crucial physical situations, of narrow electron cyclotron beams launched, in Gaussian form, either into isotropic transparent media or through anisotropic toroidal plasmas of fusion interest.