Tier 1 links are your direct authority boosters while Tier 2 links help them...

https://future-wiki.win/index.php/How_to_Find_High_Authority_Domains_in_Your_Niche_Without_Paying_for_Tools

Tier 1 links are your direct authority boosters while Tier 2 links help them stay relevant. Using Ahrefs to monitor your backlink profile helps you see how these layers push rankings up without overdoing it