1% in idle is still amazing. Unless the phone is powered down, I'm not sure how you can really get much better than that.
"Samsung’s press materials say that the phone offers about 390 hours of standby time with LTE on." - Still insanely impressive and you probably have to have Ultra Power Saving mode on, which puts your phone's appearance and operations in crap mode.
If you lost 1% every 8 hours, then you will be getting roughly 800 hours of standby, which is double what Samsung claims you can achieve.
If you are going by what the other poster said, then he/she is likely referring to having the phone rooted and applying the "Greenify" app. This will hibernate anything, including system apps. I do hope you have luck with that... for some reason, when I use Greenify on this phone, I get worse battery life than with it off. I"m too lazy to tinker with it...
How can you expect any electronic device that is ON to not have any battery consumption over 8 hours? obviously it needs to consume power to stay powered on...cpu is still running..cellphone still needs to maintain communication to the cell towers...syncing is still happening...running apps or system apps are still updating their status....