Select list showing limited contacts, using “CiviCRM Contact” reference in drupal
I see there is a limit set while building the options on the select list. It seems this has been only handled for autocomplete widget as $limit doesn't gets modified anywhere in the function or is nowhere passed to _civicrm_contact_ref_potential_references_standard() function.

So, it is set to a default value of 10 every time the list is loaded irrespective of the widget used.