Video card doesn't seem to shut down

I'm using a mid-2012 MBP. I've got 2 external monitors hooked up - 1 on each of the DisplayPort ports.

During the day I run Parallels in full-screen mode on one of the external monitors.

At night I move the mouse into the upper-right corner - which is defined as a Hot Corner to put the displays to sleep.

I've noticed that if I shutdown Parallels, or even just take it out of full-screen mode, when I go to use the machine in the morning everything is cold (to the touch) like I would expect it to be.

However, if I leave Parallels running in full-screen, then in the morning the palm-rests are warm and the bit of metal just north of the keyboard (between the keys and the screen) is hot.

My research shows that this is where the Nvidia graphics card is housed - which leads me to believe that the graphics card is not shutting down as it does if nothing is left in full-screen.

So the question is: Is there some setting that can be adjusted to allow the video card to shut down when there is a full-screen app on an external display but the displays are in shutdown mode? If that makes any sense.