How to query with more workers on a large table with many partitions

Hi PostgreSQL community,

I have a large table (86 GB) that is declaratively partitioned by year,
sub-partitioned by month, and sub-sub-partitioned by day. It currently has
437 leaf partitions, and will continue to grow with a new partition each
day. When I query a simple count(*) by date, the query planner plans a
query with five workers, but I have the following in postgresql.conf:

max_worker_processes = 12
max_parallel_workers_per_gather = 12
max_parallel_workers = 12
shared_buffers = 32GB
temp_buffers = 1GB
work_mem = 512MB

The top-level partitioned table has been ANALYZEd.

I'm running PostgreSQL 16 on an AWS EC2 instance with 16 logical processors
and 128G of RAM. How can I get PG to run the query with more workers?

Thank you,
Gabriel