Pressure not gravity. Gravity alone would cause our juice to run out the 510 connection. No, it's pressure baby! Water runs uphill with negative pressure quite easily actually. Basic fluid dynamics, first year engineering school. State O'Flux is such an engineer, a respected member and long-time friend. He knows his stuff.
With both the Taifun and Kayfun, the wicks stay immersed in the juice because of the pressure seal and negative pressure effect. It's physics and mechanics of differential pressure fluid dynamics. Does it defy reason that liquid could flow upstream? Yes, until we learn that even the Romans used devices, based on pressure, that caused water to run uphill using hydrostatic techniques that we see at every kid's science fair for the last 100 years. I'm sure you've seen these demonstrations, it's just that we don't realize this is the science behind our tank atomizers.
Of course, proper wicking plays a role in the pressure seal, as SOF points out, and that can be just tricky enough to make for difficulties at the pressure seal, particularly when we first start making coils and wicks. Materials, design, draw intensity, distance, etc. all play a role in these designs, and, as it turns out, it's actually pretty fun to play with them and learn this skill. I do wood working, and hydrostatic levels can still be found based on these same principles.
I haven't played with the GT2 yet, but I am looking forward to it! Right after my new No. 7 jointer and a new LN Jack Plane! (I've got the bug...

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I wish you well in your vape journey! Good luck!