I've got an antminer s9 running and getting pretty high rejection rate (20%). It's on vardiff and been at 16384. Should i set it to manualy difficulty at 16384? Or manually set it to half that (8192)?
What settings are people getting best hashrates using for their S9?
I don't have a sha256 miner so I can't test.
But the average rejection rate is 4.3% for the sha pool so 20% is too high.
You should try different manual difficulty for at least one hour each time.
Keep in mind that the further you are from the pool, the more reject you will have.