The stagnation plates have a strong spillover at the junction of the splitter endplates that creates a side vortex that helps the car's undertray work better in conjunction with the side skirts.
Overall, the size of the aerodynamic elements was not changed and the car's frontal area was not changed. With the sealing of excess vents in the front bumper and the ducting of air to the heat exchangers there is a possibility that the drag has been reduced while downforce was definitely increased over the previous year. A front diffuser was planned but could not be completed in time for the event.
Insufficient front downforce was a factor in the car's losing the record to two other cars, the car was clearly slower in some of Buttonwillow's high-speed turns and Dai complained of not being able to put the power down like some of the other cars in the fast run group in these turns.
The flat bottom feeds the main diffuser. The diffuser angle is relatively steep but generous vortex generators help keep the airflow attached. There is no problem with developing sufficient rear downforce, just that the car needs more in the front.
Chris Eimer built a more American style cage that triangulates all of the suspension pick up points together. This is much safer and has the potential to improve the handling as well. You can see the cage structure through the rear trunk opening.