Thanks guys, still looking for a better way though. Somebody has to know the answer over there at reakktor, I'm sure! Hopefully I can get an answer soon, as I'm pretty much done sculpting the terrain in mudbox and need to know a proper scale to move forward.

To scale the heightmap in world machine and then bring it into unreal engine 4, I need to have as close to the right size as possible. The fine details and z axis are not really important, just the size of the whole landscape and each zone. I plan to chop the terrain up into zone sized instances for the engines infinite world size feature, but need to know the whole area to bring it into world-machine first. Exporting it from world machine is what needs zone size figured, so when I split them they all match right.