Upload the rom that you save via ATIflash and I will take a look as soon as I can. (I should start a service doing this LOL)

My best result for samsung was using the 1750 straps and i get about 30MH/s with Mem set to 2150

1750 Straps
https://www.dropbox.com/s/g341nrhk8dun0ly/rx4801750Straps.rom?dl=0
1625 Straps
https://www.dropbox.com/s/dq3n2qz4t0dnecu/endermrn1625%20straps.rom?dl=0

Note: I am not responsible if you overclock your gpu to far using my provided straps or for any other reason as flashing roms can be risky so I offer no implied or expressed warranty. Remember it is always best to slowly increase frequencies to find the optimal setting for your cards.

https://www.techpowerup.com/gpudb/b3719/sapphire-nitro-rx-480-oc-8-gb
I'm almost sure that my card has 2304
cores then I install the 1750 Straps.
Do I have to install it to the cards one by one correct?