Just found this in a first drive review:
The Sonic is an economy car, which means sacrifices in creature comforts. The rear seats don’t have an armrest or cup holders, but they are acceptably habitable even behind a six-plus-footer in the driving position. Both Sonic sedan and hatchback share the same 99.4-inch wheelbase. The four-door, at 173.1 inches, is 14.1 inches longer than the hatch but loses in the space race with 14 cubic feet of trunk space to the hatch’s 19. The hatch also has slightly better rear-seat headroom. The cargo area in the five-door, although not as spacious or ingenious as the Honda Fit’s, has a removable false floor that creates a level surface when the seats are folded. There is also a slot for the cargo cover to slide into behind the rear seats.