Depends on how full the tank is when you lay it down...
Per Svoemesto's User Manual for the Kayfun... (
http://www.svoemesto-manual.de/get.php?man=4&lang=EN
Minor leaks may happen if the tank is filled completely, or it is filled more than halfway while Kayfun Lite is lying horizontally or with mouthpiece tilted down for some time. In this case, one of the grooves (1h) could be at the top "in the air" and another one at the bottom dipped into e-liquid.
In this case the air will escape from evaporation chamber through the top groove and e- liquid will flow from the tank to the evaporation chamber through the bottom groove. Naturally this process stops as soon as both grooves are covered with e-liquid. Make sure that both grooves are always covered with e-liquid, keep Kayfun Lite horizontally in such a way that the mouthpiece is always slightly higher than the evaporation chamber. Even better, keep it in the vertical (or near vertical) position if your battery mod allows it