Question Understanding Custom Post Process Orders

How does the custom post process orders under project settings / graphics / hdrp global settings actually work?

I added my own post process in the "Before Post Process", where I extract the current render buffer. However, when looking at the content of this, I can see Post Processing effects such as Exposure is already added to it.

But, how come? I thought "Before Post Process" means whatever Post Processing code would be executed before Exposure and others?

This is my code, for reference, all I want to do with it is to store the image in the renderbuffer so I can access a pure non post processed image (ignore the exposure effects, they are not important).

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering;
3. using UnityEngine.Rendering.HighDefinition;
4. using System;
5.  
6. [Serializable, VolumeComponentMenu("Post-processing/Custom/PostProcessHelper")]
7. public sealed class PostProcessHelper : CustomPostProcessVolumeComponent, IPostProcessComponent
8. {
9.     [Tooltip("Fixed Exposure")]
10.     public ClampedFloatParameter fixedExposure = new ClampedFloatParameter(0f, 1f, 15);
11.  
12.     [Tooltip("Compensation")]
13.     public ClampedFloatParameter compensation = new ClampedFloatParameter(0f, -10f, 10);
14.  
15.     Material m_Material;
16.  
17.     public static RenderTexture renderBuffer;
18.  
19.     public bool IsActive() => fixedExposure.value>0;
20.  
21.     public override CustomPostProcessInjectionPoint injectionPoint => CustomPostProcessInjectionPoint.BeforePostProcess;
22.  
23.     public override void Setup()
24.     {
25.         Shader shader = Shader.Find("Custom/PostProcessHelper");
26.         if ( shader!= null)
27.             m_Material = new Material(shader);
28.     }
29.  
30.     public override void Render(CommandBuffer cmd, HDCamera camera, RTHandle source, RTHandle destination)
31.     {
32.         if (m_Material == null)
33.             return;
34.  
35.         if (renderBuffer == null || renderBuffer.width != source.rt.width || renderBuffer.height != source.rt.height)
36.         {
37.             if (renderBuffer != null) DestroyImmediate(renderBuffer);
38.             renderBuffer = new RenderTexture(source.rt.width, source.rt.height, 0, RenderTextureFormat.ARGBFloat, 0);
39.         }
40.         Graphics.Blit(source, renderBuffer);
41.  
42.         m_Material.SetFloat("_fixedExposure", fixedExposure.value);
43.         m_Material.SetFloat("_compensation", compensation.value);
44.         cmd.Blit(source, destination, m_Material, 0);
45.     }
46.  
47.     public override void Cleanup() => CoreUtils.Destroy(m_Material);
48.  
49. }