Allows all tiers for building in all zones. Any fixes for this?

The mod has no direct support for that. You can however change the size of all zones. Make the middle zone bigger and the other zones smaller.

InnerWall - 182 | The length in meters of zone 4 will be counted from the middle of the map.
middleWall - 437 | The length in meters of zone 3 will be counted from the middle of the map.
outerWall - 723 | The length in meters of zone 2 will be counted from the middle of the map.