Where does the vent air come from?

I have an 04 Mountaineer (I bought it used in 07) and I've never been happy with the amount of air that comes through the vents when I have the ac cranking and I also think the defrost should have stronger air flow. Also, now that it's winter, when driving on the freeway you can feel cold air coming from behind the glove compartment. I took the blower motor out from behind the glove compartment and when I looked up there was a circular hole about 3" across that had leaves sitting on top of a string cross mesh. I'm wondering how leaves got there. I got what I could out but the mesh has about 1cm squares and it's hard to pull leaves through it. I was wondering if maybe leaves are blocking my air flow somewhere down the line but I don't know how outside air gets into the vents and the path it takes. Any thoughts? Any suggestions appreciated.

Lift up the hood, it's under the front plastic cowl, the rain diverter for the windshield.

Also ,see Musty smell out of car vents http://www.automotiveforums.com/vbulletin/showthread.php?t=904915