[Boydean]

I really believe they mean that the back of the BUMPER needs to be covered with fabric. If you look at the rule and shift your eyes over to "enclose the BUMPER backing (plywood)" I think this very clearly stated that the back of the BUMPER(part attached to the FRAME) must be covered.

This is how our team views is, this is how we made it. If you look at it from a safety point of view; having the back covered helps prevent splinters when dealing with the BUMPER.