We use flare effect to stop the aircraft during a normal EoL - the airflow is presented to the underside of the disc by selecting a nose up attitude which increases rotor thrust, reduces RoD and forward speed. Now try this with a 20 kt tailwind - as you pass zero airspeed you still have 20 kts groundspeed to get rid of so you pull the nose up further but nothing happens. Why? because the air is approaching the disc from behind so all the nose up in the world won't generate any flare effect. You will still hit the ground at 20 kts but with the tail striking first because you have so much nose up attitude. Or worse - you will start to raise the lever when the nose up doesn't work and hit even harder with rapidly decaying Nr.
Try a downwind approach to the hover in 20 kts of wind if you don't believe me - it takes more nose up to slow the aircraft down and more power which is the reason we teach slow walking pace for downwind approaches - flaring hard at the end because you are coming in hot will lead to embarassment.