I don't have a 40cm Obitsu, but here are some shots of Saber, one of my 50cm girls.
Here's Saber hugging her knees. This actually isn't as close as she can get; it is, however, as close as she will stay without me holding her in place. Something like a clear rubber band between her wrists might get her to huddle up tighter. But Saber just won't hold it. I guess she doesn't like this pose?
Saber: Such a position conveys a sense of weakness and vulnerability, so it is inappropriate for one of my position. A king must always display confidence!
Right...
Here's Saber kneeling. As you can see, she can't kneel as far as the 40cm can in the picture on the website. However, there are multiple reasons this might be the case.
As you can see here, the reason she can't kneel any farther isn't because of her joint, but because the hard vinyl of her thighs touches together. So, because the outer parts of the 40cm are a different shape, it might be possible for that doll to kneel more deeply.
It's also possible for Saber to kneel more deeply if I loosen the joint and pull her knee out from her leg a little ways. (Sorry the angle on this one's a little more awkward!) So that's also a possibility if you want her to kneel more deeply.
As a side note, Saber will hold this pose much better. Isn't it undignified for a king to kneel, too?
Saber: Nonsense, this pose is perfectly appropriate if one is meditating or eating at a low table.
Ah, so that's your true motivation!
Saber: Hmph.