What you can do is pull the input spreadsheet outside your "input window" and place the input on the second monitor.
When moving the input spreadsheet - as long as your mouse does not come in contact with the margin of your "input window", the spreadsheet will not dock on that margin. So, use your mouse to shift the edge of the spreadsheet outside the input window. Then click and drag the spreadsheet from a point outside the input window and locate it properly on the second monitor. The graphics will remain in the input window.
I cannot say that we have a reason to limit the input window size.
_________________________
Dave Diehl