Sparkworm

From what I understand, landcover percentage determines the ratio of land to ocean, while scale is like a multiplier for the size of both.

No, I don't think there's any way for you to adjust vanilla generation to prevent floating islands. There are some terrain generation overhaul mods that seem pretty good. These might not generate floating islands, but I'm not certain. And plenty of people do like the floating islands, though I'm not sure they fit VS as well as MC.