From OP

"Both Poloniex a Bitfinex announced that they will assign their users both ETH and ETHC after the fork. This is a step in the right direction, now it's up to these major exchanges to enable ETH/ETHC trading that will no doubt be demanded by users. Decentralized exchange Bitsquare announced ETHC trading right after the fork. Other trading venues will follow since there is a strong business case. We are in touch with several other exchanges to add ETHC trading to their platforms. If your exchange is interested in ETHC trading, please contact us.
"

Maybe Polo has an ETHC address you can mine to?

edit: I logged Polo and I don't have an ETHC address yet.

1:1 with eth at 0.0019

try set "-etha" to "0" and then to "1". From readme:
.....
-etha   Ethereum algorithm mode. 0 - optimized for fast cards, 1 - optimized for slow cards. -1 - autodetect (default).
   You can also set this option for every card individually, for example "-etha 0,1,0".
.....

If it does not help - make sure you use Catalyst 15.12. If still see higher hashrate on pool with ethminer - use it.

PS. For Dual mode: I get the best hashrate on Ethereum if I change Decred intensity manually by "+" and "-" keys at some value (press "s" to see current stats).
After that you can set best found value with "-dcri" option.

Testet it over the last night.
Made no difference for me at dwarfpool. Switched back to ethminer.
I'm on Ubuntu with 4x R9 280x.