Hi Dhawal, thanks for your answer :)
I've checked that before posting this question, but unfortunately there is no property on the sub-grid metadata related to page size. Or at least I couldn't find it.
By the way, I didn't have to use the Entity Form Metadata at all, after adding the sub-grid targeting the Document Locations entity, Portals automagically added the file list and the file manipulation buttons to the sub-grid, no further configuration was needed.
Anyway, everything I've tried to change via Form Metadata had no effect on the SharePoint sub-grid.
Regards,
Pedro