Reading through the tech regs, I think that teams are aiming the regulated last 100mm of the tailpipe up far enough from the body so the area where bodywork is not allowed (purple) does not include the nub at the end (green) to allow for the bridge (as I call it).
As the exhaust (dark blue) exits the tailpipe, the coanda effect tends to keep the air flowing along the surface (teal) and towards the corner of the floor back there, but the bridge strengthens this effect (light teal).
I suspect in this picture they’re doing a baseline test without the bridge then went out again again with it to compare like Merc GP did.
update: @brianjee says:
Yeah, pointing the ‘truncated cone’ high was Caterham’s approach