i dont know if it just my luck or lushcaves really only generate below a hill with a biome that isnt plains.

just create a world and /locatebiome lush_caves
it's consistently below elevated terrains and plus, no azelea trees generating. 

everytime you do /locate lush_caves you will most likely to be covered in stone, in a jungle or dark forest biome. i can't find a lush caves that generate in the plains or other biomes. is that a feature or bug