Well I ran out of disk space importing data for a clean load that I had already imported a month ago, on the same machine with the same import data into the same database
So I'm trying to figure out what changed, and the only thing I can think of is a few schema changes that impacted the size of the indexes somehow.
It may also be partially related to how the data is imported, I did a test on one of the indexes by dropping it and recreating it and it was 20% smaller (and that was in a non-ideal situation with zero selectivity).
Or a combination, indexes that didn't exist before plus they're not being imported efficiently.
Problem is it's not a nice empty database, even a brand new load has GB's of data and hundreds of millions of rows.