It's a slightly different question but you should be able to use the same technique as described here, i.e. use the api in your message template to look up the info:
It looks like line 669 here:
You can try changing the 12 to something else. It might work to replace it with Civi::settings()->get('search_autocomplete_count') and then it should use the value under Administer -> Customize Data and Screens -> Search ...