Deploying search results to a CPT single page

I’ve got my search and filter setup working perfectly on my front page (within Oxygen). It searchs/filters my CPT no problem.

However when I clicked through to a CPT single page I also have a new searchandfilter form/results here which basically does the same as the front page form but with an hard-coded meta_query to show related CPTs.

I have search results showing on a page but I can’t seem to action any ordering on it. I believe this is due to the ‘Results URL’. If I hard set the URL to one of my CPT urls then it works but, as you can guess, if I visit a different single page that ordering no longer works as the URL has changed.

I’ve tried to implement the below on the page but it doesn’t appear to work.

function dynamic_search_results( $url,  $sfid) {
	//if search form ID = 225, the do something with this query
	if($sfid==1636)
	{
      $url = get_the_permalink();
    }
  return $url;
}
add_filter( 'sf_ajax_results_url', 'dynamic_search_results', 10, 2 );

Can you give some guidance on how to setup a results with a dynamically changing URL.

Hope the above makes sense.

Thanks.