I’m a bit late on my reply to this one, but here’s some advice from a digital, cut sheet print operator for 13+ years, I now work installing digital presses, training new operators, and doing color analyst work.
a simple answer is, depending on the density or %value of the K channel, greyscale gradients appear somewhat grainy. The press has no choice but to separate it’s dither or dot pattern to create a halftone and essentially use the human eye to fill the gaps. The lighter the gradient the more grainy it will appear.
The solution would be to use a rich grey to create the piece. However, the press operator must be diligent in creating a neutral grey for you - and you must be diligent in choosing the correct formula to assist the operator in doing this. Asking the printer would be the best approach.
Also keep mind, neutral in one environment is not neutral in all environments. The phenomenon is called chromatism, no, not like in music, but when certain lighting conditions are either absorbed or reflected back to viewer. Tungsten lighting can make a grey appear warm, while florescent has a cooling affect.