Nissan Patrol 4x4 (Africa)

You mean like this??

The objective of all the mats etc is to create as much negative pressure inside the engine bay as possible. On my Patrol before I fitted Peter Connans bash plate, there was a plastic deflector that sat basically under the radiator and it acted like an aerofoil of a planes wing. this extra negative pressure helps to "suck" outside air in through the radiator and all the stuff in front of it, allowing the viscous fan to ensure higher volumes of air is moved trough and out the engine bay. In other words the hot air moves to the firewall and then drops down and under the car chassis.

I had to remove the plastic deflector plate when I fitted Peter's bash plate. However, on mine it does a similar function even though there are slits in it. Due to the size of the bash plate it still creates the same effect as the plastic deflector plate.
I have even considered blocking some of the slits to create more wind resistance to create even more negative pressure in the engine bay, but I need to replace the side "mats" on my engine bay too, so it would be pointless on mine at the moment.

However having said this, I wonder if the guys having water overheating problems have looked at this as a solution. Bearing in mind the positioning of the deflector (or Peter's bash plate) needs to be fitted in such a way as to multi task both protecting the necessary, and being able to defect sufficient air