How do I set the active in-call window to persist to a certain location on the desktop when it pops-up?

When you answer a call with the Lync client, you will see a new active-call window on your desktop. The location of this window is determined by its previous location. You can set this windows location by dragging it to a desired spot on your desktop and when you hang-up, the Lync client will remember this as its last location. The next time you answer a call, the active call window will persist.