People running Postgres on ZFS in Serious Production™ will tell you to set recordsize to 8k or 16k, because performance. Don't listen to them if you're just running personal stuff on VPSes with expensive storage! Small recordsize kills compressratio. So turn it up and rewrite the database with VACUUM FULL ANALYZE. (My Matrix server: going up from 16K to 128K raised compressratio from 2.11x to 3.08x! That's with lz4.)