Yes with 2 card spilt the hasrate in 2 with 3 split in 10/3 and so on
I had the same on ethOS (built on ubuntu) when mined ETH with pair of r9 380's on old s775 MoBo. Had a 9,5 hashrate on each of two cards. One alone was giving stable 18,5.
After switching to Win 7 problem has disappearerd and only thing each card does 17,5 even with some mem bust.
So what sys do you have? May be using Win can solve that problem too?
I am on windows because i failed for round about 8 hours to get amd drivers installed on ubuntu :/