lowering Terrain at run-time, C#

Hi Everyone, I'm working with a code that lowers my Terrain from a tool at run-time, which is working fine. I used a sample code that I found online and tweaked it for what I'm doing, but I want to change the size of the hole. if anyone can have any suggestions it would be greatly appreciated.

 using UnityEngine;
 using UnityEngine;
 using System.Collections;
 using System.Collections;
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 
 using System.Linq;
 using System.Text;
 
 public class TestShovel : MonoBehaviour {
 
     bool shouldDraw = false;
     public Terrain myTerrain;
     TerrainData tData;
     int xResolution;
     int zResolution;
     float[,] heights;
     public float speed = 0.05f;
     string speedString;
     public Transform myTransform;
 
     // Use this for initialization
     void Start () {
         myTransform = transform;
         speedString = speed.ToString();
         tData = myTerrain.terrainData;
         xResolution = tData.heightmapWidth;
         zResolution = tData.heightmapHeight;
         heights = tData.GetHeights (0, 0, xResolution, zResolution);
     }
     
     // Update is called once per frame
     void Update () {
         speed = Convert.ToSingle (speedString);
         if (Input.GetMouseButton (0)) {
             lowerTerrain(myTransform.position);
                 
         }
     
     }
     private void raiseTerrain(Vector3 point){
         int mouseX = (int)((point.x / tData.size.x) * xResolution);
         int mouseZ = (int)((point.z / tData.size.z) * zResolution);
         float[,] modHeights = new float[1, 1];
         float y = heights [mouseX, mouseZ];
         y += (speed / 10) * Time.deltaTime;
         if (y > tData.size.y)
             y = tData.size.y;
         modHeights [0, 0] = y;
         heights [mouseX, mouseZ] = y;
         tData.SetHeights (mouseX, mouseZ, modHeights);
         
     }
     private void lowerTerrain(Vector3 point){
         int mouseX = (int)((point.x / tData.size.x) * xResolution);
         int mouseZ = (int)((point.z / tData.size.z) * zResolution);
         float[,] modHeights = new float[0.5f, 0.5f];
         float y = heights [mouseX, mouseZ];
         y -= (speed / 10) * Time.deltaTime;
         if (y < 0.0f)
             y = 0.0f;
         modHeights [0, 0] = y;
         heights [mouseX, mouseZ] = y;
         tData.SetHeights (mouseX, mouseZ, modHeights);
     }
 }