You know, maybe we shouldn't just go by the space to determine the number of "zombies" per lost soul of a given size. They probably cram in and even pile on top of each other. So we could get the HD up to much larger numbers for the Huge and Gargantuan versions.
I guess we could do a # of zombies vs HD of lost soul table of some kind, and just say you add the number of zombies together, but I was concerned you might consider that a bit too fiddly.
Counterproposal?You read me like a book.![]()
On second thought, fiddly may be the only solution at this point.![]()

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.