About low hashrates in dual mode - it seems I need to combine some of my messages into one and add some more comments about ETH+LBC mode.

1. AMD cards always handle dual mode better than NVidia. Especially 290(X)/390(X) cards, they are the best. RX480 is good too. Other cards are not so good in dual mode.
2. Lbry is not so good for dual mode as Sia or Decred, it takes too much GPU time, therefore ETH suffers. So only powerful cards are good in ETH+LBC mode. Do not use it on 280, 270, 7xxx, etc. On these cards ETH+DCR or ETH+SIA is better.
3. My test rig: 6x390, stock clocks, gives 172MH/s ETH in ETH-only mode.
In ETH+LBC mode, "-dcri 16", it gives 167MH/s ETH + 167MH/s LBC.
If you have 290/390 cards and see big drop on ETH even on "-dcri 16", make sure you use 15.12 drivers.
So I see -5MH/s ETH but +167MH/S Lbry, i.e. dual mining is working. Unfortunately, there is no way to get 0% drop on ETH if you mine ETH+LBC. Why? See item #2.
4. Why I added ETH+LBC if it causes ETH hashrate drop? Because this mode is good anyway for fast cards like 290/390/480, you get small ETH drop but good LBC speed.
5. Why I added ETH+LBC if ETH+LBC has less profit than LBC-only mining? Because in future ETH+LBC can have more profit than LBC-only.