Comparison between τ_crit and τ_s in both the sublimation and fragmentation model for a 1.00 M_⊙ star. In the sublimation model, τ_s > τ_crit,2 for r ≲ 0.2 au, which could lead to runaway coagulation. As the disc evolves, τ_s decreases, and remains within the bounds up to smaller orbital radii. In the fragmentation model, τ_s ≪ τ_crit,1, which suggests these pebbles no longer drift and should therefore grow in situ as well. The values for τ_crit,1 and τ_crit,2 were calculated by numerically solving t_grow = t_drift.