Hi

Well, the b part is made of thin plastic, similar to body material I would say, but a bit thinner and feels a bit more brittle.

When fitted, it is pointing slightly downwards, as much as it can as it leans on the angled surface of the c part. In order for it to "close" there need to be some flow in the opposite direction.

I was a bit surprised about that because I thought it would be pressed up against the a part when it was fitted and pressed together, bit it was still pointing downwards.

I'll see if I can take it apart again and take a photo of what it looks like in static position.