When I do a refill via the top method I do it abit different and find mine does not leak on me ever (so far, hope i have not jinxed myself now), but what I do is:
1) Plug airflow hole with my thumb and take top cap off
2) Fill up only 2/3 of the way to the top. Put top cap back on 1-2 twist
3) Flip tank upside down, move thumb off of air hole and tighten cap on all the way
4) Flip tank back to normal and replace onto mod (if it was not just left on)
If I place more then about the 2/3 of
juice into the tank I will notice that when I am tightening the cap back on (while it is upside down) I can get a bit of a drip or two come out of the drip tip, so I have assumed that means it has to much
juice in it. My friend had his kayfun always leak on him as well when he top filled, and I noticed he would keep the airflow blocked with his thumb the whole time filling, when I showed him how I top filled and removed my thumb when tightening the top cap and he tried it, it stopped leaking on him... Not sure if its just the way we set ours up, but hopefully it can help you as well.