The electron screening effect was studied in the $^{1}$H($^{7}$Li,α)$^{4}$He, $^{1}$H($^{19}$F,αγ)$^{16}$O and $^{2}$H($^{19}$F,p)$^{20}$F nuclear reactions on two different hydrogen-containing palladium foils. In one of the targets we did not detect a large enhancement of the cross section due to electron screening, and in the second one we measured a high electron screening potential for all three reactions, up to an order of magnitude above the theoretical models. Contrary to the predictions given by the available theories, the data suggest that the reason behind this difference is linked to a dependence of the electron screening potential on the host's crystal lattice structure and the location of the target nuclei in the metallic lattice.