The authors study the formulation of atomic scattering in the impact parameter approximation. They first note that the asymptotic conditions for the case of Coulomb interactions are not defined unequivocally within the impact parameter approximation. They then show that any ambiguity can be waived when the impact parameter approximation is derived as the eikonal limit of the quantum equations. Finally, in showing the uniqueness of a minimal form of asymptotic conditions, they provide a proof of the celebrated prescription presented by Cheshire (1964).