[en] The angular beam velocity spread of the injected relativistic electron beam in the REBEX machine reduced in order to achieve a higher plasma heating efficiency. For this purpose, the guiding magnetic field in the diode region was increased to 1.5 T and ultrathin anode foils were used. Simultaneously, the length of the interaction region was shortened and a new plasma source with a transient reversed magnetic field was installed. In the experiments the beam energy deposition efficiency was calculated on the basis of measurements of local plasma diamagnetism. Both the single transit and the reflected beam regimes were studied. In the former case the energy deposition rate increased along the beam path in accordance with the theory, while in the latter the longitudinal profile of the deposited energy had a reversed slope and the overall beam deposition efficiency was up to 3 times higher. (J.U.) 8 figs., 7 refs