Concerning windows all the way down -
If you don't have anything to hide, then invite them to your house for a look see.
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I know a few LEO's, and respect all those who deserve it but...
I've had my vehicle checked out.
Saturday afternoon pick-up b-ball in the park, getting ready to go home, had both doors open and the trunk, drinking a soda BS-ing a bit.
CHP's come into the parking lot, do a full drive through, I hardly notice.
They stop, blocking our car. Starts off friendly with "how ya doing fellas" he asked who's car it was and talked to me. Turns out there was a report of some racing on the freeway. Mind you that we're just finishing basketball and looked like it, not only was myold beat-up 66 ford fairlane 170ci ice cold and clearly could not be the vehicle he was looking for. The whole time this question and answer session was going on the other one is looking (upper torso inside) into both sides and the trunk. I stated that I didn't understand the delay and the search. He got even more "by the book" uptight. He checked all my paper work and seemed intent on making it take as long as he could. He even checked my eyes to see if I was under the influence and mentioned that I seemed jittery asking me about methanphetamine.
Looking back, I realized that this young, short, inexperienced officer was just playing a game and trying to control me. He informed me that the other officer wasn't searching my car, but they'd be happy to. I thought of respectfully asking for the presence of a supervising officer, but this event had already taken 45 min of my life, so I kept quiet.
To wrap it up, I don't need anyone sticking their head into my vehicle looking for stuff to look at closer without just cause. I'm cool with a traffic stop, conversation w/ inquiries and any legitimate concern about contents of my vehicle. My car is my personal propery and anything more than a walk around with observation through the glass is not cool. If you were there you'd see it my way too, I'm as clean cut as... well, ME. This was just a young gun having a bad day, and taking it out on me - he was fishing.
So, I think 10 inches allows room to see/smell inside enough, but leaving it up to his (poor) judgement made me late for dinner.