after some testing i found the higher temps to be in the upper corners (near brake booster and ac canister thingy), and just above the tunnel. i wish i had taken some notes on the temps but ill be doing this again once i have the vents for before and after numbers to show these do or do not help. i have a strong feeling these will reduce temps in a measurable number maybe 5 -15 degrees maybe even more.
Can confirm your high temps in the corners by results with my vehicles ....
Theres a TJ writeup that shows the -
principles - of what happens under an XJ bonnet, here -->
http://www.oman4x4.com/hoodvents.htm
When you look at the TJ image ... there is a noticeable lack of heat in the centre of the bonnet compared to the area behind the fan, the two rear corners .... and along the firewall.
Thats coz the TJ hood is high enough above the engine ... not to wear holes in the padding
Along with a less cramped engine bay.
Googling some wind tunnel images will also give you an idea of how to make "slipstream" effects work for you.
High temps above the tunnel are to be expected being close to the engine altho that temp does lower ...
a). When the rad air intake is improved so as to flow through to the rear better.
b). When air is allowed to escape at the corners with a spaced hood ... with an induction blocker fitted.
c). By fitting a cowl hood which introduces ( inducts ) cooler air at speed ...
keeping in mind that a sensor fitted above the tunnel - will then measure the temp of that new, incoming air ... rather than whats happened to the old air ...
A benefit of the cowl hood in addition to its low speed venting action is the clearance space above the engine.
Dont know what happens with flat bonnet vents except simple physics, means they allow naturally rising heat to escape at slow speeds ..... and can turn into scoops at higher speeds if mounted in the wrong position.
Im more interested in improving overall outgoing airflow ... rather than just chopping holes in the hood ... as better outflow ensures max intake thru the radiator ... and under bonnet temps improve as a result of the moving air.