Postgres file increment size I'm COPY-ing 300 tables / 400G to PG10@win2016server using a few threads to speed things up, but because the table files are incremented in 64-kb units (or something there-about) they get fragmented on disk which hurt read performance.

Ideally I would like to make sure that files are expanded in larger increments (eg. 8 mb), alternative would be to make initial size = max segment size (1gb). Is there any way to accomplish this?

And I know, single threaded copy would solve the issue at hand, but I would still have the same problem after the copying, as tables grow continually and still only in small fragmented chunks.

EDIT:
As a "proof" of sorts, i created a simple table

CREATE TABLE testtable 
(
  id bigint primary key,
  somestring varchar(4000)
);

BEGIN
  FOR i IN 1..2000 LOOP
   insert into testtable values(i, repeat('Jeg kan en sang der kan drive dig til vanvid.', 40));
 END LOOP;
END


which produces a table of 4096kb, which contig.exe reports to be of 25 fragments (in this instance), or 160kb on average. For 4 mb this is not an issue, for 400gb it is.
NTFS is, in my experience, typically pretty good about cleaning up fragmentation as files grow. I would wait until you actually have the large files and have run defragmentation on the volume before worrying about it.

Just because small files tend to be easily fragmented does not mean that large files will be a problem.