I am unable to modify structure generation options in superflat customization

What I expected to happen was...:
Increase the size/frequency of villages and mineshafts.

What actually happened was...:
Structures generated normally, but not at the increased rate I expected

Steps to Reproduce:
1. Customize a superflat world any way (I attempted multiple) with the biome set to plains.
2. list Village as a structure to generate followed by (size=10000 distance=0)
3. Generate the world. Villages will be at the typical frequency, size, and distance

Example of codes I tried:

minecraft:bedrock,30*minecraft:stone,45*minecraft:water;minecraft:plains;oceanmonument,pillager_outpost,village,biome_1,mineshaft,stronghold,decoration,lake,lava_lake,dungeon

minecraft:bedrock,2*minecraft:dirt,minecraft:grass_block;minecraft:plains;village(size=10000 distance=9)