As name states, when using the Matrix Enchanting module it seems to be impossible to above 21 max pieces. Have attempted adjusting all config settings within Matrix Enchanting from upping base count beyond 21 to changing both max bookshelves as well as trying different amounts of physically placed bookshelves. All functions work as expected up until 21 after which it stops increasing.

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Figured it out. It wasn't locked at 21, it just won't produce any more pieces once there's enough to max all applicable enchantments for the given item and the items I was using to test just happened to total up to 21.