Hi,
in general, with good servos, you can leave the value at 70.
Some Servos seem to have a different throw than others, so with some, you get into the range of values, while with others, on the same model, you don't.
In any case, you should have the ball spacing equal all around, else you will get differentiation/intraction. You could compensate for this with the free swashplate configuration if there was no other way, though.
It's also always a compromise: if you have the control rods parallel to the shaft at zero collective, they will be at an increasing angle with increasing servo throw. If you have them at a slight angle at zero collective, they will move through a parallel position maybe at half the servo throw, then tilt the other way.
Bottom line, don't worry too much, go have fun
Kind regards
Eddi
Born to fly ...
forced to work.