We study hybrid Josephson junctions between a multiband Ba_1-xNa_xFe₂As₂ iron-pnictide and Nb. We observe that the insertion of a Cu interlayer in such junctions leads to a dramatic enhancement of the I_cR_n product, despite the weaker proximity-induced superconductivity of Cu. This counterintuitive phenomenon is attributed to the differences in Fermi surface geometries of Nb and Cu, which affect the selectivity of tunneling in sign-reversal s_± bands of pnictide. Our results indicate that the sensitivity to Fermi surface geometries provides a new tool for phase-sensitive studies and paves the way to conscious Fermi surface engineering of pnictide junctions.