Hello Virgil,
The per instance fade amount node does relate to culling. To clarify, this is a link to our documentation with the highlighted area directly relating to PerInstanceFadeAmount.
Could you please link a screenshot of what you mean by “bogus”. Also if you could link how you are handling the particle fade. UE 4.9 now utilizes a hierarchical LOD system through the use of volumes which is listed in our release notes here.
Lastly there is a new grass feature that is implemented through your materials and through a Landscape Grass Type in your content browser.
Because of these new features the old way of handling LOD’s may not be handled in the same way as in 4.8.3.
Please look into some of these new features and if you are still having problems then please feel free to post again.
Thank you,