I think the "Mean Separation Value" considers the entire cave biome, causing some caves to not generate fully anywhere near the set "Cave Biome Mean Width" if you try to lower the separation value and increase the width at the same time. Say there's two large cave biomes between 1, the one in the middle won't be able to generate that much due to how wide the other 2 cave biomes may be, imgur link below shows what I'm talking about

(it's not 18+ don't worry about the warning it's just a doodle) https://imgur.com/a/zrK4G8Y
https://imgur.com/a/9mBOtuu

To fix this, a toggle for the Mean Separation Value to only consider the center point of a biome, the middle of a cave's diameter (including height would probably complicate things) would probably fix things.

https://imgur.com/a/HKehxqO

Making it a toggle, with the default option being off, is probably the best way to go about it cause if you end up lowering the separation too much, and cranking the width up too much, there'd be a section where the two overlap. No idea what would happen but I'd assume it wouldn't be good, unless you can do like a 50/50 to make one take priority but it'd probably just be simpler to just make a warning comment beneath it.

(again not a 18+ image) https://imgur.com/a/RKWiXxC