If you want to put the BG light under/behind the platform, your BG is going to have to be in two pieces.

The kneeling behind worked well at the event, but I don't think I'd use it for portraits all that often. Nice to have the option though.

If I build something, it will probably be 12 feet wide and 6 feet deep. I'd like deeper, but I just don't have the room.

I'll probably also build it with a white floor or even a white reflective floor so I can do my hot white work with only BG paper to mess with.