I didn't scour the rules or anything, but it seems like you should be fine. Plenty of teams have control systems that extend beyond the shelf. For instance, game pads are often held by the students in the air outside of the shelf. I don't think anyone is going to care too much about the size of your control board, I'd hope they'd be able to concern themselves with more important issues like what's going on on the field.
I would, from experience, like to say that larger control boards are A PAIN. We had a 40 pound control board (yeah...) when I was on drive team, and that thing was a dog to carry around competition.
Even though it was 40 pounds, it was shiny, covered in little trophies from other teams, and it lit up. We loved all 40 pounds of it, until we had to pick it up.
