mod sculk blocks not generating in deep dark/ancient city

Getting anything to generate underground is very annoying; it's easy enough on the surface because you only need to worry about x and z, but underground you have to either turn your generation likelihood up to eleven, or start getting really creative with your generation conditions.

The basic idea is that, with a custom condition for a world feature, you can add arbitrary code that does whatever you want when a feature is placed. (I personally use this to generate needlessly complicated structures.) In your case, you could make a world feature that generates underground, searches in a vertical line for the nearest open cave, and then places blocks within a specified radius if they're exposed to air. (I assume this is the effect you're going for?) It's more complicated, but also much more efficient than just making a ton of copies of a feature just so it has a tiny chance of generating properly in a cave. 

I recommend looking into world features, and the 'place block in 6*6*6 box' procedure template, which can be modified a bit to place blocks in a radius like this, but I could also send pictures? How comfortable are you with MCreator?

you could make a procedure that runs whenever a block is placed, if that block is sculk, and there are no players within a 10-block radius, then give it a random chance to replace itself with your custom sculk block.

The player checking is to make the the sculk block was created by world generation, not by being placed by a player.