head/neck mobility mods help?

[E-Beth]

I have an Impldoll Star head on the Impldoll Model body. The head does not have the range of motion I would like. (The Model head behaves just the same on the Model body, so I guess it's a "feature")

I would like her to be able to look up and down at least a little bit.

The Model head on a Resinsoul body is great (the RS neck is smaller).

I understand that one can sand various bits and get a bit more space to move. Would one sand the socket in the head or the neck or both?

Any tips?

Thanks