Imagine the joy of that joystick when it isn't dancing around in the yoke. How soon will you whack it with your coffee mug, or drop your headset on it, when it's strapped to your leg? A BIG display in a small confine will get in the way of your hands, your elbow, your... uh... belly.
Just because you bought a large-format display, you shouldn't be punished for your act. Give that respectable navigation tool a deserved place: in line with your panel instruments. At the same time, you'll turn your portable, large-format GPS into a heads-up display!