Is 14.4 MH/s normal for a R9 270?

I started mining Ethereum coins yesterday. My rig has two Radeon R9 270 non-X's (One MSI, one Asus) at 1080/1475 MHz. Both show 99% GPU usage on Openhardwaremonitor. I'm using Genoil ethminer with these settings:

ethminer.exe --farm-recheck 1000 --cl-local-work 128 --cl-global-work 16384 -G -S us-east1.nanopool.org:9999 -O 0xDD9727f5a40ea34559fA897D0E6665aCB25eEEEB.pc --cl-extragpu-mem 64 -t 2

Currently the mining software is reporting 28.8 MH/s, which means each one should get 14.4 MH/s.
Things I tried:

1. Using different local and global work settings, keeping in mind that both need to be powers of two. For local, I tried 64, 128 and 256. For global, I used 4096, 8192, 16384, 32768, 65536, 131072, and 262144.
2. Changing the GPU extramem setting
3. Changing "-t"
4. Using different mining pools
5. Mining with each GPU individually (via "--opencl-device "

System:

• Windows 10 64-bit
  
• 8 GB DDR3 memory
  
• No CrossfireX
  
• Driver version: 16.3.2 non-beta
  

My clock speed is 1080 MHz, which is similar to what many others on this forum use for their R7 370 cards. But I think the average hashrate people report for a R7 370 is 15 MH/s. R9 270 cards have 1280 stream processors instead of 1024. So in theory, I should be getting 18.75 MH/s.
No matter what I tweak, I end up with a hashrate of 14-14.5 MH/s per card. Am I missing anything?