Two questions about AO techniques

[Ivan83]

1. Why is the skeletal mesh shaded by DFAO, although the documentation says it should not be?
   

   

2. Why is SSAO disabled for hair shading model in the PostProcessAmbientOcclusion.usf file?

*else if(SSAO_NORMAL_MODE == 1)
    {
        // full resolution
        WorldNormal = GetGBufferData(UV, false).WorldNormal;

        FGBufferData GBuffer = GetGBufferData(UV);
        if( GBuffer.ShadingModelID == SHADINGMODELID_HAIR )
        {
**WorldNormal = 0;**
        }
    }*

What is the reason for this?

Maybe I can use the similar method to disable the hair from DFAO shading?

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UE4 ver. 4.20