Nether forest biomes: Large fungi and small plants only generate on the topmost layer of nylium, leaving all lower layers devoid of flora

In cases where a crimson forest or warped forest spans the y axis such that there are multiple viable spots for trees and stuff to generate, they will always pick the highest up possible point to generate, and as such the lower layers will be completely lacking any sort of plant/fungal life.

This effect does occur on vanilla, with exaggerated results with the netherHigher mod, but is best tested using a custom superflat world:

minecraft:bedrock,2*minecraft:netherrack,minecraft:crimson_nylium,30*minecraft:air,16*minecraft:netherrack,minecraft:crimson_nylium,60*minecraft:air,32*minecraft:netherrack,minecraft:crimson_nylium;minecraft:crimson_forest;decoration

Generate the world, and on the top layer all of the trees and small plants can be seen. However, flying below the ground reveals two more layers, and both of these are completely blank, even though they shouldn't be as foliage generation has no light requirement.