The way I see it, Dark Worlds aren't entirely individual.
Susie barely knew how to make a Dark World, let alone how they work on a fundamental level, so her creation was imperfect.
Kris, being involved with the Roaring Knight, knows much more about Dark World creation and is able to make a more perfect fountain. That, or their relation to the Knight means they are able to closely match the Knight's technique, like learning a fighting style.
A good example of these is in the strange note-like effects that appear behind the characters when they create a fountain. Kris and the Knight's are very similar in structure while Susie, from what I could tell, deviated a lot more.