I think I'm doing something right. Five rigs I have mining Ethereum on Ethermine are getting a low rate of stale shares at 0-4% consistently. I'm mining with Ethminer 0.13 on these rigs with the following commands:
ethminer.exe --farm-recheck 200 -U -S us1.ethermine.org:4444 -O <My_Ethereum_Address>.<Rig_Name>
Each rig has 7x Asus Turbo 1070 with a reported hashrate of ~216 MH/s. Similar rigs mining with Claymore 11.0 (Ethereum-only mining mode) also on Ethermine are getting 3-10% stale shares.