The processing of radio sounding results from the "Mir" station during the periods when it was below the F2 layer maximum had shown the existence of new, previously unknown trace on ionograms called retarded lower traces (RLT). The analysis of this trace lead to a hypothesis according to which in conditions of such an ionosphere uncommon trajectories of many frequencies come into existence, which after the inclined reflection from Earth interact with sharp gradients of electron density in the ionosphere and as a result of this interaction return back to the satellite. The analysis of these ionograms gives an opportunity to construct the distribution of the isoelectronic surfaces inside of ionosphere irregularities. The results of mathematical modelling of the experiment are presented in the paper. The method of characteristic, is used for ray tracing calculations. Additionally, the height analysis was held, wherein the position of the satellite was varied in order to understand the behaviour of the returned trajectories and to locate optimal heights to receive ionograms with such traces during satellite ionosphere sounding. (6 pages)