Really, if water gets in its going to seek the lowest point or path. what are the odds of it's really going to be an issue. I understand your concern, but I think you're fretting over something that may not be an issue. Good idea though.
Your probably right but when I initially installed my BT4180 and breakout harness, I could not get my fairing back on without having a small gap in the vent so I threw this on "just in case". I have recently been to my dealer and noticed that all the brand new 2016's have the same little gap. Guess I never noticed it before. I also have no reason to believe my windshield is watertight at the fairing on either side so again just cheap insurance. While I don't purposely leave my bike out in the rain, it seamed that last year we rode half our miles in the rain and it always seamed to pour at night every time we traveled which is 1-3 times a month.