Heat maps of relative differences (dark blue means better agreement) and their averages between the predictions of each model (BES1, BES4, and AD, upper x-axis) and the observed abundances and ratios. Each column corresponds to a model with density n_H = a × 10^b, displayed as a(b). Top: heat map of relative differences in TMC 1-C. The best-fitting model is shown in bold. Bottom: heat map of relative differences in TMC 1-CP. The green and red models are those in agreement and disagreement, respectively, with the observed N₂D⁺ and N₂D⁺/N₂H⁺ upper bounds.