I understand your confusement, and even I was mixing the wrong things together with the right ones.
Best way for storage:
Cool(between 15 and 18 degrees celcius)
Standing up, wich means vertical
Pffff now we have been thru the wole thing I guess. Oh Nic it doesn't matter if store at 19 or 20 degrees celcius, but avoid any heat and daylight..
Confused? Yes and No, even I allowed to misled my self between horizontal and vertical...
Good luck Nic,