Using large size artboard will scale the item?

I created a large size artboard and inserted a rectange, I found the size of rectange will be scaled by 10 times.

var app = new Illustrator.Application();
var doc = app.Documents.Add(
    Illustrator.AiDocumentColorSpace.aiDocumentCMYKColor,
    27040,
    14810);
var item = doc.PathItems.Rectangle(762.5, 87.5, 300, 100); // width 300pt

the width of the rect is 3000pt but it should be 300pt.