No worries here!
What it comes down to is the tank holding the liquid in these things is a closed system with a partial vacuum. The only place air should be getting in is through that very center hole in the bottom of your coil. The only place air should be coming out is when you draw on the mouthpiece. When you draw, as air passes through it "sucks" liquid from the tank and it's partial vacuum into the wick and coil. Stop your draw and the vacuum in the tank "pulls back" a little, preventing your liquid from leaking out all over the place through the bottom. If the vacuum is working right the position you hold or store your EVOD in shouldn't really matter - if everything is working right. The lower the level of liquid is in any of these Kanger types, the less the vacuum is. You may notice less of a leaking problem with a tank half full or more, but as you get lower and lower the leaking may be more of a problem. Keeping the EVOD full helps.
You coil and wicks - including those top wicks - act as a partial stopper. The wicking prevents liquid from just flooding out the bottom. You can occasionally get a badly made coil that will have it's own "special" flooding issues. Or a coil with insufficient top wick. The solution there is to add more if needed. Having extra 1 mm silica wick is a good thing to try and correct wicking or leaking problems. (And something you will eventually need if you are interesting in rebuilding your own coils.) What also works? Kitchen cotton cheesecloth. I've resorted to that more than once - cutting, rolling, snipping a piece of it to replace a top wick.
Thinner liquids can result in more leaking/gurgling problems with these Kanger BCC's - but not always. Again, you can always tweak the top wick to suit your liquid too. It's worth a shot to try higher VG to correct a wicking/flooding problem. But there are other ways around it.
Hard draws don't usually work well or better. These are small coils, with small wicks - they can only take up so much liquid so fast. Harder draws may only get your less vapor since you will be pulling more air into the wick than liquid. Personally, I tend to hit the fire button on a Kanger device for a second or two, then start taking my first of three to four short pulls off it. Rather than trying to take one long hard pull all at once.
I'm looking but I don't see it. If it's only a small amount that falls into the realm of "normal". For all of these devices that is where air gets into the 
