Problem Standing into Objects

Okay, I have been trying to work this problem out for myself for a few days now. I have done a ton of research and trial & error and am just not getting it. I know that this is kind of a common issue with people who aren't fluent in coding yet, and I have never worked with any kind of coding in my life until recently.

I have a Run & Crouch code that works really well, and I'm trying to modify it so that I can RayCast Up from my Character Controller's center while crouching and keep the character from standing up under a Collider. I think it would be better to SphereCast instead, but I have only just started looking into that approach.

I think my biggest problem is that I'm not understanding how RayCast works.

Here's my full C# code:

 using UnityEngine;
 using System.Collections;
 
 public class RunAndCrouch : MonoBehaviour
 {
     public float walkSpeed = 5; //Default Walk Speed
     public float crouchSpeed = 1.5f; //Default Crouch Speed
     public float runSpeed = 10; //Default Run Speed
     bool crouching;
     bool running;
     float standardHeight;
     float crouchHeight;
 
     CharacterMotor chMotor;
     Transform tr;
     float dist; //Distance To Ground
 
     // Use this for initialization
     void Start ()
     {
         chMotor = GetComponent<CharacterMotor> ();
         tr = transform;
         CharacterController ch = GetComponent<CharacterController> ();
         dist = ch.height / 2; //Default Distance To Ground (Char Height)
 
         standardHeight = ch.height;
         crouchHeight = ch.height/2;
     }
     
     // Update is called once per frame
     void FixedUpdate ()
     {
         float vScale = 1.0f;
         float speed = walkSpeed;
         crouching = false;
         running = false;
 
         running = Input.GetButton ("Run");
         if ((running) && chMotor.grounded)
         {
             speed = runSpeed;
             running = true;
         }
         else
         {
             running = false;
         }
 
         crouching = Input.GetButton ("Crouch");
         if (crouching)
         {
             vScale = 0.5f;
             speed = crouchSpeed;
             crouching = true;
         }
         else
         {
             crouching = false;
         }
 
         if (crouching)
         {
             Vector3 startPos = tr.position;
             float length = (standardHeight - crouchHeight);
             
             if (Input.GetButtonUp ("Crouch"))
             {
                 if (!Physics.Raycast (startPos, Vector3.up, length))
                 {
                     crouching = false;
                 }
                 else
                 {
                     crouching = true;
                 }
             }
         }
 
         chMotor.movement.maxForwardSpeed = speed; //Set Max Speed
         float ultScale = tr.localScale.y; //Crounch/Stand Smoothly
 
         Vector3 tmpScale = tr.localScale;
         Vector3 tmpPosition = tr.position;
 
         tmpScale.y = Mathf.Lerp (tr.localScale.y, vScale, 5 * Time.deltaTime);
         tr.localScale = tmpScale;
 
         tmpPosition.y += dist * (tr.localScale.y - ultScale); //Fix Vertical Position
         tr.position = tmpPosition;
     }
 }