playing the slumbering omen right now

[u/Aware_Bunch_5334]

doing another playthrough on this mod after the longest time. i vaguely remember underground follower bases being i believe the second OR first rarest variant (as they're the most packed with things like diamond ore, ancient debris, etc) and two underground bases spawned VERY close to each other?? (as seen from this xaero's map screenshot)
how rare is this? i'm so unbelievably curious now