Below Y=0, large dripstones will only generate on the ground and will never form stalactites. To reproduce, use a single biome world and select "Dripstone Caves", then use the seed 460675293075333483 and run the following commands:

/execute in minecraft:overworld run tp @p 5634 20 4070 -112.8 0.0

Huge dripstones will generate correctly above Y=0.

/execute in minecraft:overworld run tp @p 80 -49 -1071 -34.3 1.3

Huge dripstones will only generate stalagmites when below Y=0.