JSFL - Document Properties Advanced Settings

Hey guys, I can't seem to find the JSFL properties to toggle the different anchor points for resizing the scene. We're creating a multiscreen animation and need a quick way to crop the screen to their individual 1080p sizes and I'm looking for a way to quickly do that in JSFL for faster exports. I've been trying to use document.width and document.height but they always resize the screen to the top left anchor point. Any help would be greatly appreciated.