Column density profiles of CH₃OH (left) and N(CH₂DOH)/N(CH₃OH) profiles (right) of various combinations of the introduced non-diffusive mechanisms (model ND1-ND6; upper panel) and of diffusive models, including the diffusion of hydrogen (and deuterium) atoms by quantum tunneling (model D2; red) or a diffusion-to-binding energy ratio of E_d/E_b of 0.2 (fast thermal diffusion; model D3; orange; lower panel). A diffusive model with a diffusion-to-binding energy ratio of E_d/E_b of 0.55 (slow thermal diffusion; model D1; grey) is shown as a reference. All models are performed within the framework of the single collision model. The observed profiles, ranging from the dust peak into the direction of the methanol peak, presented first in Chacón-Tanarro et al. (2019), are depicted in black (errors as grey-shaded areas). The results are presented for the best-fit time of t = 3.0 × 10⁵ yr.