  We study Josephson junctions between a multi-band iron-pnictide
Ba1-xNaxFe2As2 and conventional s-wave superconductors Nb and Cu/Nb bilayer. We
observe that junctions with a Cu interlayer exhibit much larger IcRn, despite a
weaker proximity-induced superconductivity. This counterintuitive result is
attributed to the difference in Fermi surface geometries of Nb and Cu, which
leads to a selective one-band tunneling from Cu and a non-selective multi-band
tunnelng from Nb. The latter leads to a mutual cancellation of supercurrents
due to the sign-reversal s+- symmetry of the order parameter in the pnictide.
Our results indicate that Fermi surface geometries play a crucial role for
pnictide-based junctions. This provides a new tool for phase sensitive studies
and paves a way to a conscious engineering of such junctions.
