I went in and tweaked the main style sheet. Be aware that if you do this to the main Oxygen theme and not a child theme, you’ll have to re-do it after every theme update. It takes two minutes, so I don’t mind.
Go to Appearance, then Editor. On the right are links to the many CSS pages for the theme. Click on Front Page one. To change the number of Primary posts, find this part of the code:
<?php $args = array( 'post__not_in' => get_option( 'sticky_posts' ), 'posts_per_page' => 10, 'meta_key' => '_oxygen_post_location', 'meta_value' => 'primary' ); ?>
Notice it says 10 for posts per page for my code. It will say 5 or 6 for the standard code. Change the number to whatever you want.
To make sure the page didn’t get too long for scrolling, I also changed the number of secondary posts from 12 to 6 here:
<?php $args = array( 'post__not_in' => get_option( 'sticky_posts' ), 'posts_per_page' => 6, 'meta_key' => '_oxygen_post_location', 'meta_value' => 'secondary' ); ?>
Hope this helps!