Particles are going to settle at roughly the same rate either orientation.

• Vertical storage will stack higher and have a greater distance to opening on top, causing the not mixed well enough issue.
• Horizontal storage more evenly distributes the mix for a more similar pour upon reorientation.
• Flat on it’s face would distributor even closer to even mix, but that way lies madness and is not optimal for pantry storage. [Maybe flat on top of fridge might work?]

So the spectrum will be the same at any orientation except the effect will be more or less pronounced. With flat storage leading to the least granular separation while also being inconvenient to practically store.

Least effort way: Store sideways/horizontally/perpendicular to pouring. Not vertical. Will settle to side instead of bottom and come out more evenly.