Air flow vs. rad shroud

[Hammerhead]

Ok stupid question time from the village idiot...
Which is better, open to allow the air to fully flow through the radiator allowing it to do its job, or if you watch my Rad Shroud video.
As you can see because of the large size of my rad, and the normal size of the fan, a full 1/3 or more of the rad is blocked by the very "flat" portion of the shroud, therefore not really allowing for good cooling air flow.
Yes, I know that when the fan is engaged it causes a massive suction and will draw the air through it, but man that shroud is such a massive restriction.
The fan will still draw a significant volume of air simply due the size of the fan, and since I am MM2vU'd it doesn't need to engage during regens n stuff, and I'm also APU equiped, so I don't idle much.
I am strongly considering pulling the flat portion of the shroud to see if there are any gains.
I know airflow is very significant in cooling, because back in the cabover days, the guys with them that pulled heavy weights never ran nearly as hot as the conventions due to the cab tunnel allowing the heated air to escape easily.

Has anyone tried this?
Pros?
Cons?
Do it, don't do it?
And most importantly, tell me WHY your opinion is such...

I really feel like I'm giving up almost half my rads capability. This summer has been exceptionally warm, and I'm always trying to increase heat dissipation because of my job.