I dunno if it would look good but I would use a soft brush and go between white and black.
I would paint a think line behind your last c4d used and the BG then try some smudging.
I think it's the lack of depth doing it for me.
Your render and the effects used are great but then there's just a blurred BG.
Know what I mean?
Yeah, I just blurred the BG at the end. :p
Thanks for the advice.