Attempt to explain
From Prouty
"A model helicopter mounted on a turntable in a low-speed wind tunnel permitted simulation of flight at all wind azimuths. The tail rotor was mounted on a separate support to investigate its performance at several positions with respect to the main rotor. Mounted far behind the main rotor, it suffered a thrust loss in left sideward flight due to the vortex ring state. But a position close to the main rotor produced no thrust loss — for reasons I do not understand."
Just as it is necessary to escape VRS in the main rotor by schedding it away through forward flight, the MR downwash provides for enough translational flow relative to the TR to reduce TR-VRS significantly.
delta3