For sure, there's definitely a lot of cool techniques (and I'm not aware of all of them)! And the first example is very much contrived to show a small example.

I'm not super familiar with the term index merge - this seems to be the term for a BitmapOr/BitmapAnd?

Is there another optimization I'm missing?

The article links to my code for my timings here: https://github.com/ethan-seal/ors_expensive

There is an optimization that went in the new release of PostgreSQL I'm excited about that may affect this - I'm not sure. See https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit...