Awesome! You figured out how to control the vent!
I bought the largest one that I could, cut a hole for it in my grill block and air dam, and still had difficulty keeping my car from overheating as I climbed one hill.
I do not use my air conditioning, it actually does not work right now in my Civic. I just had the vent going and the temperature gauge passed the halfway mark, so I opened my windows, and turned on the heater.
That makes driving in Arizona less enjoyable...
So, I figure that the hole is not always big enough, and the vent would restrict too much flow, even when open.