Can't get my plant to spawn in caves

From what I have read from posts about getting plants to spawn in caves all you have to do it set the plant type to cave (and add generation conditions if you want it to only spawn in caves, which I do not), right? So I've set it to cave, but they're only spawning on the surface, anyone know what the problem could be?

I've searched around a bit but haven't found anything about this (only similar topics with people having them spawn everywhere and not just in caves) so I'm having to make this post, so sorry if I've missed any existing topics about this. Just to clarify I'm not asking about only wanting them to just spawn in caves, I want them to spawn everywhere, and the problem is they only spawn on the surface and not in caves.

I've tried to get it working myself in a number of ways, such as changing the optional blocks the plant can place on to stone and messing around with the generation to make the spawn frequency absurdly high to make sure they weren't just rarely spawning in caves, but nothings worked.