I have the same Helicopter and the same Crappy Manual, IT'S 30mm, I put that Section of the Manual under a High powered Microscope to make sure it was a 0 NOT AN 8. I feel like a Forensic Scientist looking for Clues here........[:'(] Anyway whatever the manual Says FORGET IT! ON ANY HELICOPTER YOU SHOULD HAVE EQUAL MOVEMENT IN BOTH DIRECTIONS, THEN CENTER NEUTRAL! AND NO MECHANICAL SLOP, The Control Rod and control horn should be tight as a virgin, but Freely move when the servo needs to move it without any binding...........

Your Whole Problem sounds like you can't get enought positive Tail rotor pitch to counter act the Main Rotor Tourqe.
The tail rotor needs more movement or more positive pitch to bite the air and hold that heli in place! Somewhere in the linkage your tail rotor is being short changed and cheated.........[&:]

In short, I think because your linkage is not giving the tail rotor equal Positive and Negative Pitch Movement, Your not able to get enough positive Pitch on those Tail rotors! If its not going to be even for some reason, then at least set it up so your heli has more Positive pitch and less negative, I think you got the Opposite right now, But they should really be evenly set up 50% Pos / 50% Neg .......[X(]