Hi Peter,
I am sorry for the delay of this reply.
At the moment it is defaulted to fetch 10 items for public stream for your guest. I am sorry that currently there is not option to configure this but you can edit the file here 'JOOMLA/administrator/components/com_easysocial/constants.php' and look for
define( 'SOCIAL_STREAM_GUEST_LIMIT' , 10 );
and replace the 10 to number of public stream items you want to display to your guest.
Hope this help