Piece of cake and probably less cost compared to the hood vent, it sounds like the fun exercise concept lost it's twinkle

It probably would have been just as effective to put spacers between the hood and the rear hinges to raise the back end of it up ...

 

Interesting project. I thought about doing something similar but lost motivation/courage/time.

One thing you could do is buy a few USB barometers as this link describes:
Air Flow and Pressure Around Car

You could then plot out whether you actually have a low pressure area above your hood vent vis-a-vis your underhood pressure. (I imagine you'd want high pressure right in front of your radiator and low pressure above your vent to aid heat extraction).

As I understand it, the front half of the hood typically has the lowest pressure (see http://flyinmiata.com/tech/images/NC-hood-pressures.gif), but from your experience it seems like there's a point where the vent will be in front of the hood and a pressure differential will actually cause air to bypass the radiator. Hard to tell from the pics, but do you think this ebay hood has the vent too far forward? https://www.ebay.com/i/300752073566?chn=ps

Keep up the good work!

 

a whole thread dedicated to vented hoods if people want more ideas: https://www.rx8club.com/rx-8-discuss...amples-263569/
only posting it here since that thread is newer than this one.