How long is the short bus? Asking because reattachment. If it's long enough consider Mair:
There's a better diagram I should find. Mair worked on torpedoes so it translates to box vans and such. I fail to understand how people define a curve with an angle (central angle vs departure angle), but the terminal angle shouldn't exceed 22°, close enough to 45° for a full boat tail.
In your case a truncation, a box cavity or a base plate could be considered. Details in Search.