Biomes blending with Caves (read description to understand)

So there is a special list of biomes which use their blocks into 50% of caves below them, this blending goes all the way to level 0 in the world. So you have go below lets say a Badlands biome then you will see terracotta layers in at least 50% of the space below the biome, And Normal cave biomes can overlap with these as these are technically not biomes themselves.