Not the best angle, but I'd say it's definitely hanging off the back of the table. Remember - a 27" iMac is heavy - if you want the back of the stand hanging off the table, hopefully you have a wall in the back to catch it if it tips over.
I can't tell if thats a super tight squeeze though and would really appreciate if anyone has this setup, if they could post a picture to see what it looks like overall.
I have 2 27" iMacs running side by side on one. There's not much space for the keyboard in front and you are sat quite close to the screen but it works.