I have two of the Big Looks. Nothing is behind the machine. I use it on my older Bernina, Brother 1500, Janome Jem, Featheweight, and Singer Quantum. There is an extension arm made for the longer machines.
http://www.thebiglook.co/Big_Look_Models.html There is a video on the website.
http://www.thebiglook.co/
I'll measure in a few minutes and post the size.