Comment from a friend of mine in another forum:

"Putting the tailrotor so that the forward blades go up into the flow of the main rotor makes the tailrotor a little more powerful, but it won't be a night and day difference. Imagine a helicopter hovering inverted, the tail would no longer be in the downwash from the main rotor but it still had plenty of authority.

Our Lynx helicopters have the tail rotor blades going down with the wash from the main rotor. Later modifications have the tail rotor blads going up into the rotor wash."

The Lynx he's referring to are Norwegian military choppers