Hmm this puzzles me. Using Lisa I can get juggles I've discovered for Feathers on Mila and Sarah with ease but they never land on the other Feathers in this class (Hitomi, Eliot and Kokoro, I have to use Light juggles on them.) There are extremely minor differences between Cruiser (Helena) and Heavy (Gen Fu) as is the same with Light and Welter.
When using Lisa it seems to go more like this;
Feather: Mila, Sarah
Light: Kasumi, Ayane, Hitomi, Kokoro, Eliot, Alpha-152
Welter: Leifang, Pai
Mid: Hayate, Ryu, Christie, Tina, Brad, Jann Lee, Rig, Zack, Akira
Cruiser: Helena
Heavy: Gen Fu
Super Heavy: Bass, Bayman
I think hitboxes also play a massive part too, each character has a different one and I'm sure this can lead to minor juggle differences...