oh, then lawd.
i haven’t seen it done with bionicles .-.
then with your moc, i’d say add something akin to the EVA kneepad:
the black thing on his knee is supposed to be flush with the green part, when it’s standing up straight.
try and add something like this, where it overlaps/forms one thing when the leg is straight, but sort of spreads out/unfurls when the knee is bent.