I assume that you are saving from a SW dwg? If so, is your sheet scale 1:1? I've noticed that when saving .ai from a drawing, the sheet scale overrides the actual size. I don't know if that is a good thing or not?
As Jerry Van Dyke said, "You know what happens when you make assumptions, don't you?"
Actually, I was saving the AI from the Model, and I will bet that this is the difference.
This was my first request for an AI file and I never thought of creating a drawing first of the flat part.
Thank you, I will try this.