I see what you’re saying and it makes sense to me. I dont know enough about chamber design to fully know what bit on the chamber touches what bit on the ammo. But every time I’ve seen bullet setback talked about the bullet is always pushed “in” to the case.
Aaron at Sage Dynamics was the first place I heard about it. His rule of 
is 5 chamberings for pistol rounds and 1 chambering for rifles before he pulls it out of rotation.
You can search for “bullet setback” on google/youtube and there are many articles, videos, etc on the topic. Here are a few…
MAC says eyeball your ammo and if you can visually see a difference then remove from rotation.
