Through just two races of the season, IndyCar teams are still figuring out what works and what doesn't with their aero kits. Honda, after being outpaced in most of the practice sessions, were able to claim their first win via a lucky/good (depending on how you look at it) strategy call by James Hinchcliffe.
One thing we've noticed so far is that none of the Honda teams have elected to run the inner, smaller endplate which is visible on the stock aero kit rendering in the red box (upper right). This element has been left off throughout all sessions by every team. The current design teams are using is highlighted via a red arrow above.
The endplate itself is used to decrease drag by controlling how the air comes off of the wing and directing it along the wing tip vortices. This reduces disturbance in the air that would be created by "dirty air" that is not streamlined coming off of the car. The endplate also helps direct air around other parts of the car which is particularly important in front of the tire. A clean air-stream can increase car performance greatly.
With the flap setup covering the entirety of the tire (directing the airflow around the tire), the performance that would be gained by using the endplate was decided not to be beneficial to the teams thus far. They have managed to control the air wash to their liking without it.
Another picture of the endplate: