GLS is right - in an S76, moving a 90kg pilot by 6 inches results in a cg change of only 0.1 inches.
So unless we are considering an R22 where the pilot can detect a cg change induced by the instructor moving his feet back off the pedals, a change of 6 inches in the arm won't make much difference. Are you talking about a BK or something bigger?
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Helicopters --- a triumph of science and technology over common sense.