Resizing circles with depth of hands and head with kinect

I've got the kinect all working now, and am tracking my hands and head with some circles. And I've overlaid them on top of the raw video.

Something i noticed with the tutorials:
http://channel9.msdn.com/Series/KinectSDKQuickstarts/Skeletal-Tracking-Fundamentals

Is the fact that the tracking doesn't take into account how far you are from the sensor. So i've added some code that changes the size of the circles depending on the distance.

Next i need to change the code so the circles move less when you are further away. You'll see that, at present, when you get further away, they still try to fill the screen.