I know the exact height varies from skimmer to skimmer, but where do you guys like the level of the bubbles after putting the cup back in? Do you make it so the bubbles are around the middle of the overflow tube, up near the top so they can readily overflow, or down near the base? I havent got any real dark skimmate out of mine yet, only tan colored water with brown stuff stuck in the overflow tube. Am I putting the cup too low?