Might be dead area above bonnet but there would be pressure underneath, which means if you have louvres over it that pressure would exit up, so you get more air through front and out the louvres or under vehicle.

In slow driving the hot air would rise up and out.

I still like my idea of louvres hooked up to actuator which can be activated from cab.

The other idea (more feasible for me) is to put louvres in on both sides of engine in middle part and you have covers of same shape that go over them and have pins with clips to hold them on. When you drive in hot weather you just pull covers off, and if crossing river or raining etc can put them on.