How would I flip or mirror Terrain data during runtime?

I am trying to make a simple endless terrain illusion. Terrains don't scale at all with their transforms though, so I can't just use transform.scale(-1,0,0) to pull off making the clones needed for wrapping. So I'm now trying to create the terrain clones during runtime.

But I can't seem to get anything returned from terrain.terrainData.GetHeights(0,0,w,h); If I debug.log that info, I just end up getting "System.Single[,]" instead of the array data. According to the docs, from what I understand that should be returning a 2d array of the terrain data, and certainly should not be returning an empty array, in any case.

Here's the full code below. All I get when running this is the debug returning System.Single[,], followed by a IndexOutOfRangeException error. (The indexoutofrange is presumably because I have not gotten the data correctly in the first place) :

 //variables
 var terrainBase : TerrainData; //original terrain data, editor set.
 
 function Start () {
     terrain2A = Terrain.CreateTerrainGameObject(terrainBase);
     //scale 2A along the Z axis
     var t2ATerrain = terrain2A.GetComponent(Terrain) as Terrain;
     var h = t2ATerrain.terrainData.heightmapHeight;
     var w = t2ATerrain.terrainData.heightmapWidth;
     var oTerrain = t2ATerrain.terrainData.GetHeights(0,0,w,h);
     Debug.Log(oTerrain);
     t2ATerrain.terrainData.SetHeights(0,0,FlipTerrainX(oTerrain,w,h));
 }
 
 function FlipTerrainX(originalArray : float[,],heightmapX:float,heightmapY:float) {
     var nArray = new float[heightmapX,heightmapY];
     //Debug.Log(originalArray);
     //Debug.Log(nArray);
     for(var x = 0;x < heightmapX;x++) {
         for(var y = 0;y < heightmapY;y++) {
             //flip the x, but leave y matching
             nArray[heightmapX - x,y] = originalArray[x,y];
         }
     }
     return nArray;
 }

I'm sure I am just missing something simple here.

All I want to do is be able to loop and process the array of heightmaps to mirror the terrain for the other 4 versions needed to loop it forever. This error is a bit over my head, however, and searches are not being very helpful since the information I'm getting is very conflicting on if this should even work.