Sometimes you don’t want to run an RDP session full screen but you do want to want to make use of the real estate more than the default RDP settings allow you to choose. Using the RDP panel you can only select set values from the slider control, there isn’t the ability to be fully flexible.
So you have to customise your RDP session but this time using notepad instead. Generally your RDP session will load its default values from the Default.rdp file, held in your “My Documents” folder. So edit this and change the following two lines to whatever value you want, from the 1920×1080 defaults, in my case.