Air flow over the deck lid and vent(s) only part of the issue here...
Very short... Air off the roof hits the deck ~1/2 way back or more depending on car speeds. Allot of air goes off the back, some "rolls" to rear window at shown in second vent in video above. (String used affects testing and he's video.) This happens at very low speeds too. Starts at 1-2mph.
Many Years ago I bought the hype that Fiero engine bay was hot... Even had a section of my cave to remove trapped heat...
Then a got a thermal couple to measure heat in engine bay to test.
Result I found Fiero is cooled to about same a weather temp that day when moving over ~5 mph.
I then remove that section from my cave and call BS. Even most engine swaps do not need extra help to remove heat.
Many say 85-87 V6 has a blower... But many forget only on when radiator fan or AC is on to help SI alt and HEI parts. Those are in "bad" places may not get enough air flow to cool and SI alt's have cooling problems to begin with.
Using Roof Scoops may help or hurt to cool the engine bay, intercooler for turbo, etc.
At stops the scoop will "back flow" from stack effect. IOW Scoops will act like chimneys.
Low speed might actual cancel air flow. Heat is trying to move up but air is pushing down.
High speed might push enough air down the scoop.
What speeds does that happen? No clue. Many things can change the results so If tested on one car might not be valid on another car.
"Easy test" Engine hot...
You would need a remote thermometer to read engine bay temp w/ car moving at different speeds to see how scoops perform.
A helper to write data temp and speed and do this before and after.
Note: You are not reading engine temp, ECT sensor does that, but Air in the engine bay.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave