The chiral Fe-based langasites represent model systems of triangle-based frustrated magnets with a strong potential for multiferroicity. We report neutron-scattering measurements for the multichiral Ba₃MFe₃Si₂O₁₄ (M = Nb,Ta) langasites revealing new important features of the magnetic order of these systems: the bunching of the helical modulation along the c axis and the in-plane distortion of the 120 Fe-spin arrangement. We discuss these subtle features in terms of the microscopic spin Hamiltonian and provide the link to the magnetically induced electric polarization observed in these systems. Thus, our findings put the multiferroicity of this attractive family of materials on solid ground.