That spot you indicated is effectively sealed off due to the sides of the radiator, oil cooler, and body right there. I'm sure it could be a little bit better sealed with some bulb-seal or something like I used on the other side, but there aren't any gaps larger than 1/8" over there and it would have required pulling the radiator and oil cooler out of the car, so I didn't bother when I did the other side (where there was like a 2" gap).
Do small gaps like that make a significant difference? I figure the air can flow through the radiator so much easier than the gaps that it wouldn't make a noticeable difference. Sure, every bit helps, but I wasn't too concerned. I guess I can try to take another pass over the layout of things and look for places to improve the sealing. I have a feeling there are similar gaps at the top and bottom of the radiator, even with an aftermarket upper shroud that supposed to seal it off. That too could use some bulb-seal I bet.
One thing to note about the fenders... while I do have the factory undertray on the car, I do *not* have the complete factory fender liners. That means the area on plane with the undertray between the framerails and outboard fenders is open. That's a spot that would get covered if I installed a splitter. I wonder how much that effects the overall anti-lift and air extraction from the under the hood. I removed that part of the fender liners specifically because they kept getting sucked off the car and yanked under the tire at speed. So, there is definitely some air flowing through there.
