Problems with Foliage Distance Culling

Hello, I want to optimizate my rainforest, and the shadows are the main thing that slows down my PC, so I want to setup a Distance Culling for the foliage, I want the foliage dissapear very close to the camera so I can handle a little bit the shadows, but this is my problem:

As you can see, when the Cull Distance value is lower than 1000 the culling distance of the bushes stops decreasing, and I can see the same amount of bushes when the value is 1000 and when it is 1. How can I make the bushes to dissapear very close to the camera?

Btw sorry for my bad english, I’m still learning it :stuck_out_tongue: