The mechanism of harmonic generation in the interaction of short laser pulses with solid targets holds promise for the production of intense attosecond pulses. Using the three-dimensional code ILLUMINATION, we have performed simulations pertaining to an experimentally realizable parameter range by high-power laser systems to become available in the near future. The emphasis of the investigation is on the coherent nature of the emission. We studied the influence of the plasma scale length on the harmonic efficiency, angular distribution and the focusability using a post processing scheme in which the far-field of the emission is calculated. It is found that the presence of an extended density profile reduces significantly the transverse coherence length of the emitted extreme ultraviolet (XUV) light. The different stages of the interaction for two particular cases can be followed with the help of movies.