The gravitational potential governing gas infall. As the DM outskirts develop (see Sect. 2), both the virial R and the turnaround radius R_ta shift outwards, retaining the ratio R_ta/R ≈ 2. Meanwhile, the outer potential becomes shallower and ΔΦ lower from the value marked in black to that in blue. The shock position R_s slowly outgrows R, lowering the drop to the value marked in red.