In this work obstacle models for wave propagation over irregular terrain are investigated. Obstacles can be modeled both as perfectly conducting wedges or ellipses and impedance wedges and ellipses depending on the terrain structure and electrical properties. The irregularities of the terrain can be taken into account by surface roughness attenuation factor. The effects of different obstacle models, topographical and electrical properties of the terrain are calculated using Uniform Geometrical Theory of Diffraction for perfectly conducting and impedance surfaces. Results are compared to each other. It is shown that there is a significant difference between impedance wedge-wedge and impedance ellipse-ellipse models for low target altitudes. To calculate propagation factor precisely ellipse-ellipse model must be used for some types of terrain geometries.