[bug]Precomputed visibility worse than Occlusion culling

Hi guys, I notice a wired problem in my project.
The precomputed visibility culled far less meshes that dynamic occlusion culling.
In the example below, the static culling drop ~200 meshes, but occlusion culling could do ~1000.
That will result in high view visibility time in mobile, as the second image shows.
I really wish precomputed visibility could cull as much as the occlusion culling.
Here is my shoot:
Brown is precomputed visibility, green is dynamic occlusion culling.