Memory overhead of a large number of partitions in the same table

I would like to understand how much can partitioning can contribute to
memory usage in Postgres backend processes.

My application mainly runs SELECT statements in a partitioned table. The
table is partitioned by size (100K rows per partition, 730 partitions in
total). However, each Postgres backend process to run these SELECTs takes
~300 MB in memory, which seems a lot compared to what I've seen around.

work_mem is set to 16MB, so nothing too crazy. Also, I am using Pss to
measure the memory used by each backend process so that shared_buffers
don't mess the whole thing. Here's the output for a couple of them

Pss: 1260383 kB
Pss_Anon: 305501 kB
Pss_File: 199 kB
Pss_Shmem: 954682 kB

Pss: 1247796 kB
Pss_Anon: 293041 kB
Pss_File: 200 kB
Pss_Shmem: 954554 kB

Is this expected? Or the overhead of partitions should be smaller in terms
of memory consumption? I'm using Partman to partition the table.

Also, shared_buffers for this instance is 25GB with a total of 60GB memory.
I can provide output for explain (analyze, buffers) if needed, but the main
index used for queries is fully in memory (it takes around 18GB of space).