Weird results after Procedural Terrain Splatmapping

Hi all,

I am currently working on assigning different textures to a terrain based on their height value. I use the awesome work from https://alastaira.wordpress.com/2013/11/14/procedural-terrain-splatmapping/ as a reference for this. This works quit well at this point but it does not seem to be consistent.

In the above image the left hand side of the pillar like terrain (red circle) has the correct textures assigned but the right hand side is way off and I can't find why.

Below is the code handling the texture assignment:

 Dictionary<HeatmapLayers, float> heatmapColorThreshold = new Dictionary<HeatmapLayers, float>();
 heatmapColorThreshold.Add(HeatmapLayers.DarkBlue, 0.165f);
 heatmapColorThreshold.Add(HeatmapLayers.LightBlue, 0.33f);
 heatmapColorThreshold.Add(HeatmapLayers.Green, 0.495f);
 heatmapColorThreshold.Add(HeatmapLayers.Yellow, 0.66f);
 heatmapColorThreshold.Add(HeatmapLayers.Orange, 0.825f);
 heatmapColorThreshold.Add(HeatmapLayers.Red, 1f);
 
 
 //init Terrain
 GameObject terrainObj = new GameObject("TerrainObj");
 TerrainData terrainData = new TerrainData();
 terrainData.size = new Vector3(0.5f,2f,0.5f);
 terrainData.heightmapResolution = 128;
 terrainData.baseMapResolution = 128;
 terrainData.SetDetailResolution(32, 16);
 
 /**
 add terrain collider and so on
 big loop setting the heights
 adding textures to terrain
 **/
 
 //set alphamap to same size as terrainHeightsMap, makes fiddling with the heights easier
 terrainData.alphamapResolution = 128;
 
 float[,,] splatmapData = new float[terrainData.alphamapWidth, terrainData.alphamapHeight, terrainData.alphamapLayers];

 //iterate through alphamap
 for (int y = 0; y < terrainData.alphamapHeight; y++) {
     for (int x = 0; x < terrainData.alphamapWidth; x++) {

             //get height from terrain height data which was filled earlier
         float height = terrainHeightsArray[x, y];

         float[] splatWeights = new float[terrainData.alphamapLayers];

             //if height > orange threshold make it red
         if (height > heatmapColorThreshold[HeatmapLayers.Orange]) {
             splatWeights[5] = 1f;              
             //if height > yellow threshold make it orange and so on
             } else if (height > heatmapColorThreshold[HeatmapLayers.Yellow]) {
             splatWeights[4] = 1f;                
         } else if (height > heatmapColorThreshold[HeatmapLayers.Green]) {
             splatWeights[3] = 1f;                   
         } else if (height > heatmapColorThreshold[HeatmapLayers.LightBlue]) {
             splatWeights[2] = 1f;
         } else if (height > heatmapColorThreshold[HeatmapLayers.DarkBlue]) {
             splatWeights[1] = 1f;
         } else {
             splatWeights[0] = 1f;
         }
 
         // Sum of all textures weights must add to 1, so calculate normalization factor from sum of weights
         float z = splatWeights.Sum();
 
         // Loop through each terrain texture
         for (int i = 0; i < terrainData.alphamapLayers; i++) {
 
             // Normalize so that sum of all texture weights = 1
             splatWeights[i] /= z;
 
             // Assign this point to the splatmap array
             splatmapData[x, y, i] = splatWeights[i];
         }
     }
 }
 
 // Finally assign the new splatmap to the terrainData:
 terrainData.SetAlphamaps(0, 0, splatmapData);

I am very thankful for any kind of advice helping me finding my error.