In the case of Shanks you can see how the AdvCoC of his sword leaks, in the case of Zoro it does not. Against King you can see how the AdvCoC of Zoro's swords is filtered in several scenes. That is the difference.
Luffy tells you that he wants to learn to hit without touching. And Hyo shows it to him.
And here they explain to us that there is still another technique that allows you to introduce your CoA into the enemy and cause greater damage even with an explosion.
Zoro seems to have learned the second technique and maybe that is the key to cutting anything, doing it from the inside. Although Zoro does it in a very basic way and only with drawing techniques, that is why Shi Shi Son Son is one of his strongest techniques, said by himself.