Unity Physics Collisions Happening Despite Being Disabled in Collision Matrix

I've got a weird issue in my game where a collision is happening DESPITE that specific interaction between the two layers being disabled in the Collision Matrix (images attached).

• The Projectile is on the PlayerProjectile layer.
• The NPC/Entity is split thus:
  • Capsule Collider (Layer EntityMovement) for colliding with ground, etc
  • Unity Primitives with their own colliders (Layer NPC) for hit detection etc

I have the following code used to debug as well:

    protected void OnCollisionEnter(Collision collision)
    {
        Debug.Log($"Collision between {LayerMask.LayerToName(gameObject.layer)} and {LayerMask.LayerToName(collision.gameObject.layer)}");
    }

The output is

Collision between PlayerProjectile and EntityMovement

but this should be disabled.

I have checked and double checked the layers on the objects in question, and they are correct/as intended.

My game object setup is probably a bit complex but when boiled down, this seems like it should be simple, yet for some reason it doesn't work.

What am I missing?

check the hierarchy. if the object you given the collider doesn't have a rigidbody attached, then it will go to the parents and looks for the rigidbodies. check if the layer set on the rigidbody in parent is what you expect it to be. if you want children have a different layer then you have three options

1- give all of the children rigidbodies

2- make an object in the same position of parents and make all of the colliders children of that. then write a code to fix the position of this object as the parent

3- make a parent for all the children under your rigidbody and give a rigidbody to that.