I think you're going to have to demonstrate that it's not working. Something reproducible with actual numbers.
Crossfire was a big disappointment to me also, i run 1 card most the time. on Mantle it gets me a boost but only on that API is it noticeable , i should have got 32 GB ram instead.
i have 1000w psu
you usually get 5-10% and thats hard to notice on low FPS in the first place.