Configured Features often spawning above-ground or on bedrock roof of my dimension.

I have a dimension called The Undercroft and I plan to add many biomes with features in them.
Just so you know, the dimension is an all-cave dimension (kind of like the nether) and doesn't have a skylight, only a ceiling.
Normally, features would generate on the highest point of the world, but I want them to generate on the blocks inside of the dimension and not on the bedrock roof.
Some of them do generate inside the dimension's borders, but are oftentimes floating rather than grounded...
Please someone help 😭  I'm out of ideas...