Separate scrollbar in the document editor

I’m not sure if I’ve got the wrong setting or I’m just missing it, but the scrollbar appears to be for a specific height of the document editor window and then scrolls down to the story bible. If, however, I have my cursor active within the document, I’d like either a separate scroll bar for the document scrolling itself, or for the mouse scroll wheel to honor scrolling but within the document window only. Right now I believe I need to use the down arrow key to continue with scrolling within my document.