Jump Further When Key Is Held Down

I'm trying to make my player jump further if they hold down the W key. However, it appears that my player will always jump the same distance. I've been trying to figure this out for a rather long period of time now, and have not been able to find an answer yet. Thank you much for any help!

 using UnityEngine;
 using System.Collections;
 
 public class JumpInC : MonoBehaviour {
 
     private float distToGround;
 
     //Height of jump
     public float jumpHeight;
 
     //To allow fo slopes
     public float skin;
 
     //How fast player is forced down.
     public float jumpDown;
 
     public bool jumping = false;
     
     void Start(){
         // get the distance to ground
         distToGround = collider.bounds.extents.y;
     }
 
 
     //Is the player grounded?
     bool IsGrounded() {
         return Physics.Raycast(transform.position, -Vector3.up, distToGround + skin);
     }
     
     void FixedUpdate () {
 
         //Jump
         if (Input.GetKey(KeyCode.W) && IsGrounded()){
             rigidbody.AddForce(new Vector3(0, jumpHeight , 0),ForceMode.Impulse);
             jumping = true;
 
         }
 
         //Jump Further if Held Down?
         if (Input.GetKey(KeyCode.W) && jumping == true){
             rigidbody.AddForce(new Vector3(0, 1.5f * jumpHeight , 0),ForceMode.Impulse);
             
         }
 
         //If W is released, jump shorter distance
         if (Input.GetKeyUp (KeyCode.W) && jumping == true || IsGrounded ()) {
             jumping = false;        
         }
 
         //Push player downwards
         if (Input.GetKey (KeyCode.S) && IsGrounded() == false) {
             rigidbody.AddForce(0, -jumpHeight * jumpDown, 0);
             jumping = false;
         }
     }
 }