Distribution of the evolutionary phases of donor stars at the onset of mass transfer for systems in the fiducial model. On the y-axis, we show the number of simulated systems. Each coloured bar corresponds to a different evolutionary phase: main sequence (MS), Hertzsprung gap (HG), first giant branch (FGB), core helium burning (CHeB), and asymptotic giant branch (AGB). The hatched grey overlay indicates the fraction of systems in each category that result in a stellar merger. Error bars (shaded regions) represent the range of values for the stellar mergers across all model variations.