Repro steps :
- Open attached project
- Open scene called "Outside"
- Select the decal and move its opacity
- Do it on the Plane and on the Ocean separetely

Expected : Nothing should change
Result : The result change slightly on the water and when Additive decal blending on classic geometry

Additional info :
- The normal used is uncompressed neutral normal 127/127/255
- Result is different on Normal geometry when using Additive blending (So probably linked to surface gradient)
- Need to check if repro in older versions

Environment :
- Windows 10
- Unity 2023.1.0a26
- HDRP 15.0.3