This contribution seeks to make progress in our conceptual understanding of different ventilation pathways. To this end, we combine the examination of flow boundaries with a trajectory analysis of the actual origin and fate of air masses in idealized scenarios. Flow boundaries are identified based on finite-time Lyaponov exponents in synthetic data of TC-like vortices. Using synthetic data allows us to sweep the parameter space spanned by shear magnitude, shear vertical profile, vortex intensity, and vortex radial wind profile. The results are largely consistent with expectations based on simpler, two-dimensional models: Environmental air is pushed closest to the storm center at those levels where the ratio of the shear-induced storm-relative flow and the strength of the TC’s swirling winds is largest. Results of a series of full-physics simulations of idealized TC-shear scenarios with varying vertical shear profiles are interpreted in the light of the flow boundaries. Trajectory analysis of the thermodynamic properties of inner-core convection reveals that the actual ventilation is modified by convective-scale motion that is not well represented by the synthetic data. While flow boundaries provide one useful conceptual building block, further processes, on which we speculate in our conclusions, play a role in determining the prevalence of different ventilation pathways.