I have found a bug with Sim-Ethereal while experimenting with the sim-eth-es example. When changing the zone_radius in GameConstants.java the client gets incorrect position updates.
I stepped through the code and found the issue but it has already been fixed on master so maybe you could push a release?
While debugging i found another bug which only shows when using a zone_radius with different x and y extents:
This line should be corrected to:
return minZoneId + z * (xSize * ySize) + y * xSize + x;