Ah that's why the Bonnet gets so warm because the hot air gets pulled away from it.... ;-) in traffic or at 10mph there is not a lot of pressure difference to pull the hot air down and away, I understand your science but I can't see it's plausable in a road cars average situation. Best let the hot air escape and use the fact hot air rises to help assist with this issue.
Quick, let's all raise our bonnets to let that hot air escape when we are sat in traffic.
I stated they are a myth - in performance terms, I must apologise for not defining that.
You are wanting to help your under bonnet temps when sitting at traffic lights - I didn't know that. Good on you, being conscious of that fact cars dont tend to overheat when stationery, but want to try and fail safe that.
Science doesn't apply to normal road going cars, you're spot on.
Irrespective, it's your project, good luck with it.