Speculation and cause to think?
Lastly I'd like to talk about the images below, this shows the top flap from behind, initially I thought that perhaps I was seeing a reflection but after looking at a few different images it would appear that there is a gap at the trailing edge of the top flap. This leads me to believe that the top flap is hollow, and may be being used to blow airflow increasing the efficiency of the wing. If so how are they getting the air to the wing?
We don't usually get to see a close up shot of the car motionless with DRS open so to further fuel speculation in this image I've also added an arrow to the part of the wing that remains in position when DRS is active. This also appears to be hollow but what significance does all this have? Without being able to rationalise how a high velocity airstream could be channeled I'm simply leaving the evidence here for others to look at whilst I try to find more.
Is it however plausible that these hollow sections attached to the Endplates act as a fluid switch elsewhere and McLaren are using DRS for a secondary function (DDRS) just as Mercedes are with their Front Wing system.....
I found it strange that McLaren although their hydraulic DRS mechanism remains unchanged (albeit a new wing design) decided they would leave access panels in the endplates. Does this mean that the panels hide DDRS tubing? Maybe not but as a team that sometimes borders on anal in regard to aesthetics I find it remarkable the Endplates were not designed as normal for the hydraulics. The hydraulics are usually routed through the Beam Wing via the mounting below that as you can see carries 4 pipes (2 are plumbed in and the 2 higher ones are not in place as is the cover that usually hides these pipes from sight.