Okay so my kayfun lite v2+ isn't fitting on my hcigar caravela .... There is a big gap.
I had an HCigar Caravela clone with an authentic Kayfun Lite Plus and had the same problem you have.
The fix is real easy ... You have a gap between the mod and the atomizer because the pin in the Caravela's top cap is too long.
Remove the pin (it will screw out of the plastic insulator). Then file it down slightly to make it shorter.
Keep shortening it a little at a time until the gap it pretty much gone when the Kayfun is screwed on tightly. Just don't shorten the pin too much, or it won't make an electrical connection.