As said in the description.

While standing on the border between two chunks, if there is no visible hole to the outside environment (defined as being able to see an area that is visible to the sky) and you are facing generally away from the chunk behind you and are using the Quake Pro FOV, the chunk behind you will not render.

I have included two images, both taken in the same spot facing the same direction, but one "indoors" and the other with a hole leading "outdoors". As can be seen in the screenshots, when "indoors", chunks behind you will not render. When "outdoors", chunks behind you will render.

My video settings are also included in an image below.