Early_Z for Masked Material at Mobile shader path

Development Rendering
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1

When I enable the early_z of masked material under the mobile shader path,I found that the force early_z in shader is disabled when VT is in effect at the same time.I want to know why this is done?

// Force early depth_stencil for non-masked material that use VT feedback
#if (NUM_VIRTUALTEXTURE_SAMPLES || LIGHTMAP_VT_ENABLED) && !(MATERIALBLENDING_MASKED || USE_DITHERED_LOD_TRANSITION ||OUTPUT_PIXEL_DEPTH_OFFSET)
        #define PIXELSHDER_EARLYDEPTHSTENCIL EARLYDEPTHSTENCIL
#else
        #define PIXELSHDER_EARLYDEPTHSTENCIL
#endif