The trunk us connected to the top, rear of the engine bay under the hinges for the engine covers and between the pair of them have a fairly large cross section yours still has the box like structure that they connect to but it is blanked off at each end. I believe that some hot air travels under the floor cavity and exits through the pipes either side of the rear doors too. As far as I know, the problem with the beehives is not their size, but rather that they cause the hot air to stagnate in the engine bay, as the forward movement if the vehicle tries to force air in to them, while the fans try to force it out. I guess that as a simple and cheap test, you could try removing them before a road test and seeing if it still overheats? The other option would be to try shrouding them, much like the radiator on the Mk 3 and 6, leaving a sufficient gap for the air to escape. Some cardboard and tape should do the trick, for a test.
Cheers,
Terry