Yeah, Ive noticed the same thing, the GPU only seems to use 50% of available power. I have done nothing with Wattman, mostly because I dont know how. Is there something I should try?
I have exactly the same problem with my Rx 480 8GB. I have noticed in Wattman graphs that every 2 seconds (or so) my gpu usage drops to 0 (chip/memory clocks stays at their peaks). This is true for other games also (BF1/Battleground/SWtOR/BF4).
Is this normal? Or the card is faulty?