Particular collider not working properly...

Hi, I'm working on FPS and currently making raycast bullet which hits against colliders. This is working, but now I found colliders on my enemy character is doing something wrong.

This is my enemy character. Those colliders were added by "Create Ragdoll" and I manually adjusted a bit. It's not very precise but colliders seem reasonable...

...but this is what happened. My bullet ignores its torso colliders (the white lines are tracers left by my bullets). It's the same for other parts on this model. I have to emphasize that:

1. My bullets perfectly works fine with other colliders, such as added cube/sphere objects or the terrain.

2. Weirdly, my bullets SOMETIMES hit. So this cannot be a mistake of layermasking or something.

3. Making those collider much bigger actually helped bullets to hit, but still they seemed smaller than their visual representations.

It seems like those colliders are way smaller than it looks or in wrong position. When I dropped a cube on this model's head, it collided, but the cube made it way into his head and landed somewhere about half the radius of the head's sphere collider. This degree of inaccuracy is not acceptable!

Can anyone explain what's going on and what can be done to make things work, please?