The old MILSTD for cyclic force gradient is:
Force gradient for 1st inch of travel 0.5 to 2.0 lb/in;
Force for 1st inch >= breakout plus friction;
No undesirable discontinuities;
Positive slope with 1st inch >= remaining slope.
-and-
Limit control force <= 8.0 lb (fore and aft) & 7.0 lb (lateral)
In semi-plain english:
Force gradient for 1st inch of travel 0.5 to 2.0 lb/in;
Force for 1st inch >= force required to initiate control movement, so as to provide positive centering;
Force should increase without jumps, notches, or catches as you displace the control;
The first inch of travel should require more or equal force to any subsequent inch of travel, but the force required for displacement should continue to increase (positively) the further you displace the control .
-and-
Over the normal range of control displacement from trim, the maximum force the pilot should feel is 8.0 lb (fore and aft) & 7.0 lb (lateral)
Hope that helps some. In practice, the mechanical characteristics of a helicopter vary from machine to machine, and type to type. If the control doesn't require positive, increasing force to move away from the trimmed position, if the control force doesn't increase smoothly, and if the force is too high - the pilot won't be able to fly "care free" and there is either something wrong with the design or the specific aircraft.