Probably no front intake for this F-duct in the Ferraris. It must be less sophisticated than Macca's. Notice also how there is less space to manipulate the air where the tube from the cockpit meets the one in the shark fin.
Maclaren probably has some sofisticated fluidic switch above the airbox. This one looks more just very long pipes connected through a T section.
The air enters by the intakes behind the airbox. The pipes then split in two sections, one going to the cockpit, the other to the rear wing. Probably so that the section going to the cockpit has a larger cross section, so naturally most of the air would follow that path, and maybe a flow diverter, like this:
That's just a basic scheme and wild guessing. Naturally, most of the air would simply vent into the cockpit due to the different cross sections of each pipe, but it you close that vent, pressure quickly builds up and the only exit is now the rear wing. This also avoids having to pass two pipes in and out of the cockpit.
As usual, Ringo gets the concept faster than me
Rivals, not enemies.