Prevent sorting and dragging of specific postbox metabox

I'm attempting to limit the jQuery sortable functionality on certain postboxes/metaboxes when editing a post/page.

So far I've enqueued my custom .js file in admin.

wp_enqueue_script

function jm_load_scripts($hook) {
    if( $hook != 'edit.php'  $hook != 'post.php'  $hook != 'post-new.php' ) 
        return;
    wp_enqueue_script( 'core-functionality-script', plugin_dir_url( __FILE__) . '/js/admin.js' );
}
add_action( 'admin_enqueue_scripts', 'jm_load_scripts' );

I've created a metabox with an added class of "not-sortable" then in the custom .js file, set it's sortability to 'cancel'.

jQuery

jQuery(function($) {
    $(".meta-box-sortables").sortable({
        cancel:".not-sortable"
    });
});

This prevents the user from moving the metabox, but sibling metaboxes can still be dragged above to then push the metabox out of it's position.

I found another solution I found this question 13885665 which suggested using the code below

$( ".meta-box-sortables" ).sortable({
    items : ':not(.not-sortable)'
});

Which makes complete sense and I found the same solution advised around the web, but in this case it disabled sortable functionality on all metaboxes.

My next thought was I may be overwriting the setting that adds the .postbox class to the sortable options field items: . So I changed the code to the following.

jquery

$( ".meta-box-sortables" ).sortable({
    items : '.postbox:not(.not-sortable)'
});

A solution that I found frequently, specific to WordPress, was to disable the admin javascript postbox.js which I don't think anyone trying to disable the sortable functionality of a metabox would want to do as it removes lots of functionality.

One more solution I feel needs to be considered Question 2474. But It doesn't seem to be the way to go either.

I'm not experienced with jQuery and haven't spent much time customising the WordPress admin. I may be missing something obvious but after some time looking at similar questions and studying both the jQuery-ui Docs and specifically the WordPress wp_adminjspostbox.js file I can't move any further.

I've been asking the question due to it's specificity to the jQuery-ui on Stackoverflow.

stackoverflow Questions

Question 1 Question 2

Away from WordPress I can get sample examples working as desired, but now adding this to my WordPress solution is where I'm stuck.