Efficient electron injection into nanoscale devices is difficult to experimentally characterize at the local scale. We discuss here how little modifications of the electrostatic potential landscape in the vicinity of a nanodevice injection leads can drastically enhance electron transmission, by tuning semi-classical trajectories and directly re-orienting charge flow in the desired paths. In this context, quantum rings (QRs) appear as interesting geometries since, in a semiclassical view, most electrons bounce against the hard-wall potential of the central QR antidot directly after injection. We found that a local partial depletion of the QR close to this hard-wall can counter-intuitively ease ballistic electron flow. On the contrary, local charge accumulation can focus the flow on the hard wall potential and increase back-scattering. Simulating current density distributions in the ring gives insights on these peculiar transmission conditions. Using a voltage-polarised scanning gate to tune in situ the ballistic electron flow in a QR patterned from a high mobility 2D electron system, we find a remarkable direct experimental confirmation of this particular phenomenology.