*All these numbers are made up*

Lets say the chance to unbox a relic is 2%, and you have a item set that gives you 100% relic chance find. This does not give you a 100% of receiving a relic, it adds 100% to the chance that you will find one (100% on 2%), Thus increasing your chance to 4% overall. In the same way that if you have a 150% rare set and the chance to unbox a rare is 4%, your chance will be increased to 10% (4*150%).

Hope this helps explain this to you and again, none of these numbers i use are real, just for examples

~Bing :3