Lou, I am going to give you an educated guess. As you size down the neck, there is a slight bulge that is ever so tiny right at the bottom of the portion that does not get sized.
I hope this makes sense.
The neck expands to chamber size, then you size it down. The size down is a major deal with your chamber and it creates a small bulge behind the part that is getting sized down.
Things can get complicated as you try and get this very small doughnut sized down.
Others have given you great advise. Contact me if you get out of your mind over this.
Your sizing die deals with two dimensions:
a. base of the case to shoulder dimension
b. dia of web
You have introduced a c. into the equation, the part of the neck that is not getting sized and you are actually trying to size the brass by closing the bolt.
Lou, there are a multitude of solutions, and C & H are world class dies...make no mistake about that fact!
Keith
