Thanks Buck, unfortunately my Kraken (Fasttech clone) doesn't have a screw on the bottom. I have a Hcigar clone of the Kraken and it will not fit flush either. I went back to using my Stingray (clone) and it fits perfect.
I have seen other Caravela's that came with about 3 different 510 screws to make tanks be flush, but haven't found a place where I can buy the parts. So far, everything I've seen makes you buy the whole mod. Not able to buy only the parts.