The anchor config option being anything besides UPPER_LEFT makes the minimap disappear. All other position-related configs are default.
Using map_atlases-1.20-6.0.2
supplementaries 1.20-2.8.1
moonlightlib 1.20.2.10.9

The do work tho it's likely they are not set up properly so it renders too far to the right

Do the offsets need to be negative?

yeah if you mess with those other offset the map will eventually go back where you want. acnhors are just some additions to the offset numbers

After much trial and error, I found good values for LOWER_LEFT. Posting them here for others: