Fabman
Children Of The Corn
The placement of the louvers on my car has most of the water draining in between the radiator and engine. I have had the louvers on the car for 3 years now and have had no issues with water. I have even tracked the car in the rain. I wouldn't worry about rain in the slightest.
My car is track only so it was not A consideration for me.
I mounted my louvers a few inches behind the usual location to:
1) cover up some holes left over from the hood scoop and
2) draw some air past the blower.
The sweet spot is from 17" behind the leading edge of the hood to 12" from the base of the windshield, so there is lots of room for discretion.
I went 20 1/2" back. Well within the envelope.