What's the best way to control window size ?

I’m currently using Cubase 7 with Windows 7 Pro.

If I drag the main Project Window to fill the screen so I still have the vertical and horizontal sliders visible, then select one of the other editor windows, the Project Window changes size again ?

To get around this I select full screen by pressing the icon on the top right hand corner of the Project Window but then every other editor I load goes full screen.

Is there any way around this problem - I would like the Project Window to remain large but allow other Editor windows to be scalable.