Dig system work but some explanation

Hi guis i have made/modify a code to make a dig system it work but when i dig the hole is shallow how can i increare not the radius of the hole but the depth

public TerrainData tData;
private float[,] saved;
private float[,] prova;
public Texture2D cratertex;
public int xRes;
public int yRes;
public Vector3 mousepos;
Ray ray;
public float distance;
RaycastHit hit;
public Color[] craterData;
public Texture2D snowTxt;
public Transform cam = Camera.main.transform;
public bool ManiOccupate = false;
public bool shift = false;
public int Snow_Count = 0;
public bool inizializzaVar = true;
	void Start(){
tData = Terrain.activeTerrain.terrainData;
		xRes = tData.heightmapWidth;
		yRes = tData.heightmapHeight;
		saved = tData.GetHeights(1,1,xRes,yRes);
		craterData = cratertex.GetPixels();
	}
void Update(){
		if(inizializzaVar){
			tData = Terrain.activeTerrain.terrainData;
			xRes = tData.heightmapWidth;
			yRes = tData.heightmapHeight;
			saved = tData.GetHeights(0,0,xRes,yRes);
			craterData = cratertex.GetPixels();
			cam = GameObject.FindWithTag("LocalCam").transform;
			inizializzaVar = false;
		}
ray =  new Ray(cam.position, cam.forward);
		distance= Vector3.Distance(transform.position,hit.point);
		if (Physics.Raycast(ray, out hit,10000)){
		mousepos = hit.point;
		}
		#region Scava
		if (Input.GetMouseButtonDown(1)  !shift  distance <= 35.5 /* Snow_Count <= 4*/){
			int x  = (int) Mathf.Lerp(0, xRes, Mathf.InverseLerp(0, tData.size.x,  mousepos.x));
			int z  = (int) Mathf.Lerp(0, yRes, Mathf.InverseLerp(0, tData.size.z,  mousepos.z));
			x = Mathf.Clamp(x, cratertex.width/2, xRes-cratertex.width/2);
			z = Mathf.Clamp(z, cratertex.height/2, yRes-cratertex.height/2);
			float[,] areaT = tData.GetHeights(x-cratertex.width/2, z-cratertex.height/2, cratertex.width, cratertex.height);
				for (int i = 0; i < cratertex.height; i++) {
				for (int j = 0; j < cratertex.width; j++) {
					areaT [i,j] = (areaT[i,j] - craterData[i*cratertex.width + j].a/60000);// dividi per diminuire il diametro del buco
//					Debug.Log("i:  "+i+"j:   "+ j );
				}
				}		
//			tData.SetHeights(x-cratertex.width/10, z-cratertex.height/9,new[,]{{0.000001f}});
			tData.SetHeights(x-cratertex.width/2, z-cratertex.height/2,prova);		
			Snow_Count++;
		}
}

how can i do??

It’s c# xD