Hi Reuben
I guess you are talking the viewable right?
In this case it's 42" using gt 700 projectors at 4 feet back.
In 16:10 mode you get and image 67" wide by 42" height you then take away the overlap 12% and multiply by the 3 projectors and you get 176.88" or just under 15 feet by 42” image.
This keeps the pixels as close to accurate in aspect ratio and uses the most pixels available buy the projectors.
You can get more height using 4:3 or by pulling the projectors back but your overlap will be larger and lose more pixels to fix this you get a wider screen.
Hope this helps.
Regards chris
Pixelwix