Typical size of gas cells as a function of gas density (at t ∼ 300 Myr) in all of the simulations making up the resolution study. The characteristic length scale of Bondi accretion r_Bondi = 2GM_BH/c_s² for a 10⁴ M_⊙ MBH in T = 10⁴ K gas is indicated by a dash-dotted black line. The two horizontal regions emerging as r_acc decreases corresponds to the geometrical refinement strategy inside r_ref and r_acc, respectively, adopted in Sect. 2.4.2.