We employ a three-body classical trajectory Monte Carlo (CTMC) method to calculate the recoil-ion momentum distribution at its kinematic threshold in ion-atom ionization collisions. We analyse how this threshold is intertwined by dynamical constraints to the electron capture to the continuum cusp in the electron double differential cross section. We compare these calculations with those from a full quantum-mechanical description and explore how these structures depend on the interactions among the three particles in the final state.