Enormous Lightmaps for Foliage in 4.6.1

Hey all, I have found that building lighting on 4.6.1 on my level now yields a .map file that is 1.1Gb (UE4.5 was only around 400Mb) and has severely impacted the FPS.

I believe it is due to the lighting changes in 4.6.1 with how foliage is dynamically lit. To test this I removed the InstancedFoliageActor from my level and rebuilt lighting and found the .map size to come back down to 400Mb and FPS returned.

I’ve played around with the ‘Cast Dynamic/Static Shadows’ settings under the ‘Show Instance Settings’ in the Foliage paint tool with no luck.

Might anyone know what my issue could be?

Is it a large level? It’s not recommended to use baked lighting on a large level because of the large number of lightmaps and the amount of disk space it would use.