1. The "height" is based off the variation. If you want it flat, the height will be low, if you want it high, then you need variation. It's a chicken and egg problem.I've been having success finding taller maps, but I keep on running into two issues. 1.) The height variation is too great. For example, I can generate a world that is 600' tall at spawn, and 10' tall at the ocean, how can I make world height more consistent? 2.) Oceans are screwed up, all oceans I generate are FAR too small to even function as an ocean biome, the beaches are always far too large. I think this may actually be a bug, screenshot here shows why this is a problem: http://imgur.com/a/PqqLE
2. That looks bad, I'll have to find time to figure out why that is happening.