You mine at 2048 difficulty? How do you know what difficulty is a good rate for your mining rig?
just make sure that you can submits 5 to 15 shares per minute.
When I look at the pool, it says I have 240s/s, I'm guessing that's 240 shares per second? I mine at 512 difficulty with about 15mh/s rig. Is 512 too low?
That's 240 shares of value 1 per second. So with 512 diff, it's about one share submission every 2 seconds.
Difficulty doesn't matter that much. Let the pool choose it for you.