I used Ethermine for 5month straight, was always really close to calcs most times I would even earn more then Ethermine calc too.
Only reason I changed to flexpool was return time. 133ms for Ethermine, 33ms for Flexpool where I am.

What % are incorrect and what % are stale. Are you using AMD card or Nvidia? Maybe oc settings not the best?
So many things can change pay rates like others said before.