Take a good look at the setup next to the multimeter box, bottom of the vert row, you can see the flush rivets and the countersunk nutplate, and the cover piece with the countersink all in relation to each other.
When a flat head screw is inserted here, the cover will be flat on the bulkhead frame, and the outer surface of the cover will be smooth.
Not the greatest photo, but best I could find on short notice.
Hope this makes it a bit clearer

__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."