[X/Fe] ratios as a function of the atomic number Z predicted at the stellar surface by the models where one ¹³C pocket is introduced at the end of the TDU episode after the 12th TP as compared to the observations of each of the four post-AGB stars indicated in the panels. We normalise both model predictions and observations to meteoritic rather than photospheric solar abundances for the elements heavier than Fe (Asplund et al. 2009). Notably, this modifies the observed [Pb/Fe] upper limits reported by De Smedt et al. (2014) by −0.3 dex. The black line represents pocket_case1, which produces a similar pattern as that presented by De Smedt et al. (2014) with a high Pb abundance. Pocket_case2 is shown as a black dashed line. The coloured lines represent pocket_case3 (red) and pocket_case4 (blue). (The colour version of this figure is available in the online journal.)