The actual placement of the C4Ds is alright, but the blending and depth just aren't there. Lets parts slip behind the render [Which looks poorly rendered or perhaps you poorly erased the C4D going over the top of it] and let parts come over the top. Not sure if the render was like this originally, but what's up with the top left on the fist? Looks to be random smudging against the flow covering up parts of it.