Of course there are a multitude of variables we don't have access from the outside, but Postgres only compresses data that is TOASTed, and based on your description of the table, the data is not being TOASTed (and therefore not being compressed).

Instead, if you could somehow pack your timeseries entries into an array, you would get the benefits of compression automatically.

Given your write performance requirements, using an array may be out-of-question (and you may get too much overhead from dead tuples) -- but who knows? Always a good idea to benchmark.

I actually considered mentioning this at the post but figured it was too long already and could be the material for a future one :)