Distribution in the e−log P diagram of the observed post-AGB binaries (top), Ba dwarfs (middle), and Ba giants (lower panel). The different lines delineate the orbital parameters for which a primary of radius 250 R_⊙ (solid line), 350 R_⊙ (dashed line) and 450 R_⊙ (dotted line) fills its Roche lobe. These radii correspond to the maximum radii typically attained by solar-metallicity AGB stars of initial masses 1.2, 2 and 3 M_⊙, respectively. Both components are assumed to have 1 M_⊙ at the time of the RLOF, although the exact masses do not meaningfully affect the lines. As expected, lower primary-mass systems can reach shorter periods without RLOF.