2D: Why aren't my raycasts conforming to their origin points?

I've been testing some things with raycasts, but ran into an issue in which my raycasts don't appear to be adhering to their origin points. Basically, any movement alters where I think the raycasts should be starting.

Below is my simplified script; feel free to try this out in a new project (your character game object should have a box collider, and a rigidbody2D set to kinematic):

 using UnityEngine;
 
 public class RaycastTest: MonoBehaviour
 {
     public float speed = 5;
     public float gravity = -10;
     public LayerMask collisionMask; //Don't forget to set a layer to collide with
 
     private BoxCollider2D boxCollider;
     private Vector2 velocity;
 
     private void Start()
     {
         boxCollider = GetComponent<BoxCollider2D>();
     }
 
     private void Update()
     {
         float input = Input.GetAxisRaw("Horizontal");
         velocity.x = input * speed;
         velocity.y += gravity * Time.deltaTime;
 
         CollideVertically();
 
         transform.Translate(velocity * Time.deltaTime);
     }
 
     private void CollideVertically()
     {
         Vector2 origin = new Vector2(boxCollider.bounds.center.x + (velocity.x * Time.deltaTime), boxCollider.bounds.center.y);
         RaycastHit2D hit = Physics2D.Raycast(origin, Vector2.down, 1, collisionMask);
 
         Debug.DrawRay(origin, Vector2.down, Color.red);
 
         if (hit)
         {
             print("collided with ground");
         }
     }
 }

CollideVertically() draws a single ray downward from the center of the character's box collider (I use boxCollider.bounds.center for this). I also add what I thought represents the "delta movement," or change in the character's velocity this frame, when setting the ray origin ( boxCollider.bounds.center.x + (velocity.x * time.deltaTime) ).

The problem is that the ray seems to lag behind the character when the character is moving left or right, and is displaced heavily on the y-axis when falling. If I set the ray origin using transform.position this no longer occurs (keep in mind you still need to add the delta movement value to your x velocity), but only if I also call CollideVertically() after transform.Translate(velocity * time.deltaTime) in Update().

Am I doing something wrong? Is Debug.DrawRay just showing me an inaccurate representation of my raycasts? Ideally I'd like my rays to follow my movement exactly, never altering their origin positions. I have read articles on game collisions that mention you're supposed to move first and then check for and resolve collisions. I appear to be doing the opposite here, and frankly I'm not sure if that's the right approach when using raycasts.

Here's an image showing what I mean (notice how the ray is NOT in the center of my collider in the game view on the right): https://imgur.com/a/oouf6lp

Also, you'll notice two red rays in the scene view; it's almost like the ray is "spazzing out" as it tries to get back to its intended position.

Here's another example with more rays (not included in the above script) that really shows why this might jeopardize my character's movement (I have gravity set to 0 here, and am moving left): https://imgur.com/a/ZoQI3HU