Loci of the optical admittance of GRIN thin films are studied. We have investigated by means of the computer modeling, how the trajectory of the loci will change if the layer will have a different inhomogeneity coefficient. During the modeling we have employed a method of discretization of the GRIN layer by dividing the layer to sublayers which have equal thickness and constant refractive index. We have also examined how these loci will be affected by absorption in the layer, determined by different values of the extinction coefficient. Layers are assumed to be deposited on the bare glass substrate or substrate with a quarter- or eight-wave optical thickness layer. Results may be applied to the interpretation of the monitoring signals of the thin-film optical monitors.