Reading the first section in the “Lit Translucency” documentation page, it seems that the issue described may be related to the parameters listed at the top of the page. You could try adjusting those values to tune the distance at which lit translucent materials fade, including:
- r.TranslucencyLightingVolumeDim
- r.TranslucencyLightingVolumeInnerDistance
- r.TranslucencyLightingVolumeOuterDistance