This is Trek, we use these sort of discrepancies to solve things all the time. This one just happens to fit well.
http://www.ex-astris-scientia.org/sc...borg_ships.htm
The article says that the Borg Cube from TNG was a "massive" ship with no specific measurements. Compared to the VOY Cubes where the specifications are given.
Hell, that shot YOU used doesn't match up with other shots in BOBW itself. Like when they fight the Cube for the first time or when they fly away from it when it's self-destructing.