I have now adjusted vardiff to push up more agressively than down, that should help with this.
It doesn't help. We need ~0.2 diff
Maybe use string in password to force higher diff?
What kind of hashrate is 0.2 optimal for? For ~22Mhs vardiff now settles at about 0.14 and this means 4 shares/min, anything above is probably prone to generating quite a few stales.
I'm seeing diff 4.xx & 2.xx now. It gives 1Mhash/s more per 280x (rig with 4x 280x)
So:
diff <0.1 - 9.60Mhash per 280x
diff 0.1-0.18? - 9.63Mhash per 280x
diff 0.19+ - 10.55Mhash per 280x
diff 2.xx, 4.xx - 11.4x Mhash per 280x