Can't raise head of humanoid

I’m having trouble giving the humanoid characters in my game a custom neck length. No matter how I change the CFrame of the neck Motor6D the head stays in the same place.

Below is a screenshot of my humanoid characters in my game:

Is there a trick to getting the head of a humanoid to a certain height?

try changing the “Neck” Motor6D C1 value

Thats what I have been changing. I set the size of the humanoid with Humanoid:ApplyDescriptiomn() and then I can’t move the head in this way anymore.