Is the difficulty default too high?  My 30 MH/s worker keeps showing as offline on the dashboard, and I'm also not getting many shares that often (15 shares in 4 hours!?).

How can the difficulty set lower for my lower-hashing workers?

I have a worker that is doing 128 MH/s and getting a share every 10-15 minutes.  Seems like a slow rate of finding shares, too.