If you fully close the Custom Direct Select (Tab 39), the array size resets to default (5x10).
It feels like this should persist through a session (until power down) at least. Not quite a bug, not quite a feature request ;-).
Eos 18.104.22.168 (macOS 11.4 / Windows 10 / Eos Ti / Gio)
Thanks. This has been written up.