Get true artboard size with "large canvas" document from ExtendScript

The latest release of Illustrator adds a new "large canvas" document  for any artboard created that is larger than 227 inches in width and/or height. What it appears to be doing behind the scenes is actually changing the document scale to 1/10 of the original size.

I have an ExtendScript extension that gets the document dimensions via app.activeDocument.width. With the new "large canvas" document, the dimensions returned are 1/10 their actual value. 

For example, if I create an artboard that  is 400 inches wide by 300 inches tall (so lustrator uses a "large canvas"), when I check the size of the artboard using app.activeDocument.width it returns 40 instead of 400.

Is there a way to either detect when a "large canvas" is being used, or to get the true dimensions of the artboard?