The answer about your query regarding BP and the fast guys is simple: it's not the BP that's making them faster, but their experience. They've learned more than just BP during their time on the track, and you're seeing the results of that. I usually have pretty good BP, and some people who pass me do so with their heads where the outside mirror would be they're so crossed up, or they're not really crouched down.
There are some BP positions that change the bikes functionality, and it takes adjustment on your managing the bike to get used to it. With time you'll become more comfortable at leaning and cornering, and you'll have worked on your BP so that you're at their level. Just try to mimic what they do slowly and you'll get the hang of it, and when it comes time for you to make some bigger adjustments, you'll be able to do it without much thought.
Take a few riders for example. Haga will never get all the way down to the tank. He just doesn't. Mladin and Hodgson have almost the same BP, and it's horrible as far as professional riding goes. You can put Larry Pegram in that group as well. Spies and Lascourz get all the way down like you're probably talking about, and they're both doing great, but who's to say they wouldn't do as well if they were sitting up more.
I saw Aquino race out at Firebird Raceway in Phoenix, and he had good BP, but he didn't look anything like Josh Herrin, as he does now. I'm guessing same coach.
It's only advice, but I'd recommend making small adjustments to BP and focusing on those drills. I've spent lots of time focusing on BP, and yesterday watched a friend who put his focus on riding race in the amateur group. He was mixing it up with the advanced riders, and will be an advanced racer next season. And his BP sucks.