Reflection-absorption spectrometry has been used to obtain infrared spectra of micrometer thick films on metals. The theory and practice of this method with very thin films is well understood, but with thicker films the bulk properties of the material must be taken into account. The influence of incidence angle and polarization on the spectra that are obtained from this method has been investigated, from both an experimental and theoretical viewpoint. An incidence angle of the pseudo-Brewster angle of the film (similar to 60 degrees) with p-polarized radiation produces spectra that are the most faithful to what is obtained via transmission spectrometry.